As a follow-up note to Dave's very pertinent article in the latest Scots n' Water regarding transmission failure, the failure as Dave noted is almost always due to overheating the ATF fluid and then the resulting slippage and hard part damage. An external ATF oil cooler from the factory (often part of a 'tow package') is the best option and second would be an aftermarket ATF cooler. Today's vehicles are not very conducive to the installation of an aftermarket ATF cooler, so an excellent third option is to change your AFT fluid to synthetic ATF fluid that meets your particular vehicle's specs. Two well known and trusted brands are Mobil 1 and AmsOil and do not use any additive unless specifically called for by your Owner's Guide. The fluid typically retails for around $11 a quart and will darken after installation, which is normal. Avoid any blended synthetic ATF. The synthetic fluid has a higher boiling point and offers a far greater measure of protection against heat and hard part failure. Even with an external cooler, synthetic fluid is an excellent investment in longevity of your transmission.