You probably change the oil in your car or truck regularly. Most people follow a schedule to get this done or do it themselves every few months. Have you given any thought to changing the automatic transmission fluid? This lubricant works very hard and is subjected to lots of heat and pressure every time you drive. Just as your engine cannot run without oil, the transmission will not work without fluid. The fluid is a lubricant and cooling aide to the many complicated clutches and gears of a transmission. It should be changed on an interval as recommended in your manual, but at least every 30,000 miles.
One way to assess the fluid is to carefully pull the dipstick while the car is running, wipe and reinsert, then pull to check the fluid level. You should wipe a bit on a white paper towel and check the color which should be a clear red. You can also smell the fluid for traces of a burnt odor. If you see more brown than red color and smell any burnt fluid it is important to change the fluid right away. If your transmission has been shifting hard or slipping between shifts you might be able to save the high cost of a rebuild by changing the fluid. You can find transmission service at most oil change facilities and there are many shops that specialize in this. It is worth the cost to change transmission fluid and possibly save your transmission.
There may be a difference in the pricing of fluid changes, and this can be due to the method used. Some shops will suck the fluid out of the transmission with a machine and then simply refill it. This does not do what you really need. There is old fluid in the transmission that the machine will not access that will mix with the new fluid added. The only proper way to accomplish this change is to drop the transmission pan, unless you are lucky enough to have a screw in drain plug. Some vehicles have a drain plug and a screw in external transmission filter which makes the job much easier. Without these items the fluid change will be more involved and certainly messier. There is an internal filter that should be changed or cleaned when you change fluid.
In most cases you will not be able to do this at home. If you are able to lift the car sufficiently and have the correct tools you might accomplish this service, but for most it will be a challenge. In any case the transmission takes a lot of fluid and the filter is more costly than an engine oil filter. You should expect to pay anywhere from about $100 for an average car to $200 for a larger truck or SUV for a professional service. You should be sure to check the internet for coupons and specials, check the cost to change transmission fluid and save some money on this often ignored, but still very important maintenance.