The 4T65e on your 1998 Park Avenue is not without issues. Though GM published a variety of design improvements through its product life cycle, there are things that seem to help the 4T65e to last.
Here are the ones that I've done on all of my cars with the 4T65e..
- I installed a separate cooler for the transmission. It's controversial if these help the trans last longer but I think they do and its not difficult to install.
- I installed a 'TransGo Shift Kit 4T65E' shift kit. More specifically, I only installed stronger 1-2 & 2-3 accumulator springs & piston travel limits (both are accessible through the pan). I recommend taking the time to make those two pistons fit well & move free & smooth. These are not difficult to install, you just need to take your time and be organized.
- I prefer to spend a little extra and install a pan with a drain plug.
- This is not an issue if you re-use the original gasket (which is very thick due to the gasket's metal core). If you go with the after market gasket (which is thinner), you'll need to add a flat washer under the head of each pan bolt because the threads on the bolts do not cover the full length of pan bolts.
All the above can be done on a Saturday.
- Finally on the transmission, I prefer to use tuning software like Jet, HPT or EFILive (I prefer Jet) to fine tune ** the transmission shift points, shift timing and upshift torque reduction. It took some trial-and-error to learn how to optimize these settings but if anyone decides to adjust these, I'll be glad to share my settings and explain what each change did for me.
** This is especially significant on your 1998 because prior to about November 2002, the 4th gear hub spline was not hardened. Eventually, it will strip and loose 4th all together. I have found there is a relationship between altering these settings and prolonging the life of the 4th gear spline, I can create a write-up if anyone is interested. Though I've owned (4) cars with 4T65e transmissions, my first was a 2000 model year. That was when I became aware of the 4th gear spline issue. I was not willing to overhaul the transmission, so I turned 4th gear off all together and drove with 1st, 2nd & 3rd + 3rd TCC. Which actually still made for a good driver. Since then, I've worked to avoid this problem.
