The major killer to these trannies is the pressure control solenoid. If that goes it'll start slipping, and then banging in to gear. If you catch it early, not much damage is done. But if you let it go then it can toast it.
There are other issues that come with age (like TCC lockup function), but they're probably a little less common. This page has info on all the issues that we see out of these transmissions:
4T65E Transmission Info
The owner of that site goes by "Trannyman95" on here. He is probably the most knowledgeable person you'll find on your transmission.
Originally Posted by Sabrewings
