Well the biggest killer to a auto trans is heat. So a good temp gauge would be #1, not the joke the factory put in in 03 and onward, get a real trans gauge. If you tow I would go ahead and add additional cooling. I run the 6.0 and have never seen above 190 and even that was when I was backing up a 10K TT uphill for 45 min!!! Next is a tuned valvebody, the factory one is set up for very long and drawn out, smoooooooth shifts. A tuned VB will shorten these shifts, less contact on these clutches means less wear and also less heat. The last thing is optional and depends on how many miles is on your trans and how it has been driven, but to you can upgrade the torque converter to a heavy duty 3 disc unit. I haven't needed to take that plunge yet.