I've owned many 4t65e transmissions. And I am MAST ASE cert
If you keep these boxes cool you will get 300k out of one but here's the thing!
Get yourself a Scangauge2 and enter the transmission code to monitor your fluid temp asap!
In a car. Buick Chevy. With a little cooler you should be at 170-180 with 95 f ambient temp. Don't worry about winter months as it will get up to 140f with no problem.
In a heavy loaded van. Venture etc. you will need a big cooler! Or maybe two normal sized coolers just to keep the temp at 170-180f because of the oversized Torque converter.
remember trans fluid only lasts 30 mins at 280f.
At 220 trans fluid starts breaking down.
OUCH!
If your running a 195f engine thermostat replace it with a 180f!
Keep the underhood temps as low as you can get it this is where the scan gauge tool shines!
I've had codes 1811
It's Not a worn out trans! It's bad fluid and heat!
Long shift times etc and made the trans-should ft kit my self with bushings from a local hardware store for 6 dollars. The kit is 30 online. Accumulator spacers!
bottom line take care of the fluid every 30k. And keep it cool! I like 175f after an hour of driving! They are great transmissions with very a sensitive PCM! Any shift that is longer then .75 of a second it will set your trans code! fluid thickness plays a big part when it's super hot! It's like water so takes longer to build pressure as with cooler fluid! Spend the few bucks and time now and your transmission will take care of you.