I have a 2002 pace car. This is not a supercharged model and is just the series 2 3800. I beleive I have the 4T65E 4 speed automatic transmission. It has started to slip and shift hard, and I am thinking of replacing instead of rebuilding. I am thinking of changing to the 4T65E-HD that comes with the supercharged 3800. This is a higher gear ratio and known to be stronger. What I am needed to know is if it will work or not since they are both electronically computer controlled. I am hoping it can be just swapped out with the same wiring harness and all. Please let me know if you have ever heard of this swap before. Thanks

 

Depends on the year, but also you'll need a tune + different passenger side axle.

Truthfully, the parts that are different in the HD and non-HD trans are not the parts that are known to fail. If you want to save money, I would just gamble with a junkyard 4t65e with lower miles, or just rebuild the one you have.

A few years ago I did the same thing. Got a junkyard transmission thrown in for $400, with half the miles than the bad one in my car.

 

You're correct.

Two things:
-its numerically a lower ratio (3.29 vs 2.93) which isnt going the right direction IMO on a NA 3800. Itll make it take off slower at the benefit of lower cruising rpm. Also keep in mind if you swap the converter / flexplate to the HD as well, you'll lose a few hundred rpm of stall speed - also going in the wrong direction for performance.
-As Chibi mentioned, the differences aren't worth it. The issues with your trans now can happen just as easily on a HD. The biggest difference in terms of strength is the differential (which is a fairly rare failure point on the 4t65 aside from those doing frequent 1 wheel burnouts). If you really wanted to, you can always swap the diff / diff cover / passenger axle and get that upgrade on any 4t65.


If you're really after a stronger transmission, buy one built by triple edge performance. Theyve got a bunch of different levels depending how crazy you want to go and they address the actual weak points.

Being you've got a NA 3800, keep in mind that stronger doesnt necessarily mean more reliable in terms of mileage. It's still going to wear out like most any 4t65 over time with enough mileage.