Some other indications of low fluid level are...
Delays engagement into gear...Fluid will expand when hot..so this is more prevalent when the vehicle is cold.
(Delays into gear with the proper fluid level can be due to internal hard seals or external electronic problems)
Droping out of gear around turns. The low level causes the fluid to slosh to the side around turns, exposing the pickup and sucking in air.

What Type of Fluid Does Your Transmission Use ? If you don't know the answer, you should find out. Many newer vehicles use specialized fluid. Introducing the wrong fluid can cause damage. So if your vehicle is one of them, You should purchase a few quarts and put it in your trunk with a funnel. (If your vehicle has no dip tube, don't bother) just get Triple A.
The last thing regarding Fluid. It doesn't evaporate...If It's Low...Your Leaking...Get It looked At...Or keep it up to level until you can.

Broken Half Shafts (CV Shaft) On front drive vehicles are often mistaken for transmission problems. A easy way to tell the shaft is broken is the car grinds going back into park. (since the wheel is no longer attached to the transmission the breaks cant stop the rotation.)
Also in some cases the speedometer will register even though your not moving.
And it may still roll when in park

No Reverse in most cases is a major internal problem. But on some vehicles such as the Dodge Caravan with a over drive transmission, It can be due to the TCM...Transmission control module (Computer) or solenoid body.

No Forward Movement Before you call a tow truck, try unplugging the main electrical harness at your transmission.
Why?... First you need to understand that most 4 speed automatic transmissions use 2 solenoid's to shift them. Example ["A" on "B" off...first gear]["A" on "B"on...second gear]["A" off "B" off...third gear]["A" off "B" on..forth gear]
On most electronic transmissions both solenoids off is second or third gear, so by unplugging the transmission is may be possible to move in that gear and limp into a garage or at least get off the highway.

Vehicle Doesn't Shift Not shifting is a whole lot better than shifting and "Slipping". Be aware that on many vehicle again such as the Dodge Caravan, if the TCM senses one of many different problems it will put the vehicle into "fail-safe or Limp Mode" which is to say the vehicle will default to one gear and stay there...Giving you the opportunity to "Limp" it into a garage. Limp mode can be due to major or minor problems....The NOT SHIFTING is not the problem...But the result of another problem.
Other causes of No Shift are..Defective input or output speed sensors..The Vehicle has to know how fast it is going in order to knows when to shift.
The Transmission Range sensor (formally the Neutral Safety Switch) It tells the TCM what range your in, Reverse, Drive Low..If your in drive and it things your in low...No shift !
That's just a few of the No Shift causes...But the point is there is a good chance it is NOT a Major repair.

Slipping on the other hand, unless the fluid is low, usually is a major repair. The amount of heat given by slipping clutches is tremendous. That is why the fluid smells burnt. The big issue today with lots of aluminum and plastic parts in the transmission, is the damage to additional parts because of the heat. Since the more you break is the more you pay...Realize it won't fix itself and get it looked quickly.

Most people know that worn tires slipping in the snow can cause transmission damage, But did you know on auto 4 wheel drive vehicles having one tires pressure just a few pound less than another can destroy a transfer case ?
Here's why... The four wheel drive is activated when the wheel speed sensor sense a slip...one wheel turning faster than the other...but if a tire is under pressure, it is also smaller in circumference. this causes the sensor to think its is slipping, over working the transfer case and destroying it. Note: Mismatched tires will have the same affect.

Shift Timing and Feel
Early or Late shift speeds and hard or soft engagements.
Where older vehicle used a modulator or cable to time and adjust shift patterns, most new vehicles are now controlled electronically.
A common complaint is a late shift from third to forth gear. But on closer observation the transmission is shifting from first to second to forth.The lag where third gear should be makes it seem like a late shift.So pay attention and count the shifts or manually drop to third and see if it slips.

Transmission Fluid Pressure is also controlled electronically and in some cases hard shifts are due to the strategy of the TCM when it senses a problem.In some cases Pressure is increased to clamp down tighter to help eliminate a perceived slip.
What you think is simply a hard shift can require a complete rebuild to correct.

The Transmission Front Pump Seal (Front Leak). How much to fix a front leak ?
This is a question that will burn you just about every time. Why?...The problem is when your transmission comes out of the you'll be told the front seal alone will not correct your leak. That is because the bushing in the pump and its fit to the torque converter are critical in sealing the front of a transmission. Also in many cases there are underlying reasons...and treating the symptoms without finding the cause is a waist of money.
In a Nut Shell...If the vehicle isn't worth the cost of a full repair...don't get lead down the "hope springs eternal" path. Most shops Know it won't work...But a few will not tell you... hoping you'll go for the rest of the repair.

Clogged Filter
A clogged filter is the hope of many...but seldom the case. If it is clogged it's usually clogged with the guts of the transmission. The most common symptom of a clogged filter is a high pitch whine, the sound of the pump straining to pick up the fluid.

Low Antifreeze Level And Transmission Damage.
Transmission fluid is cooled by being pumped thru lines from the transmission to a separate cooler inside the main reservoir of the radiator. The fluid is not air cooled, but cooled by contact from the antifreeze against the cooler wicking the heat away. Low antifreeze in some setups will cause loss of contact and no cooling and overheated Antifreeze even if it is making contact, does not cool. So next time you drive your overheating car, remember it's not just your engine you can damage.

Transmission Repair in a Bottle.
They are as real as genies in a bottle. Most are solvent or petroleum based and act by swelling seals. The problem is they don't have a brain and don't know when to stop swelling. I've had transmissions with seals so swelled that the unit would not come apart, costing the customer a substantial core charge. Even if it does works, it's temporary at best.
It is a great gimmick though. I've asking enough customers if they were going to try to get there money back, the answer is always "NO". So ...If you want to put 50 cents worth of solvents in a bottle...sell it for $7.00 and get no complaints...at least in this life...