Thread: Supercharged GT vs GXP Transmission problems

I just bought a 2006 Grand Prix GT (supercharged) 2 months ago from a GM engineer, she took very good care of the car. I bought it with 68k miles on it and immediately got a transmission fluid and filter change and coolant flush. When I called the dealer to make an appointment I expressed my concern that I heard a flush can damage your transmission and they said the way that they do a flush empties out 100% of the fluid including the TC but "there's no way it will damage the transmission, it will only help it in the long run" So I opted for that and didn't notice any changes in shifting but I did notice my transmission fluid never gets hotter than 160F, (used to run around 190) and I know the cooler a transmission runs the longer it will last. I've heard horrible stories about GXP transmission problems, and I know the HD trans in my car is the same one in the GXP, and was wondering if the GTPs/06+ GT's are plagued by the same transmission problems in the GXP, and also what more can I do besides a fluid change to make the transmission last longer?

A flush is never a bad idea, as long as its maintained. As a "GM Engineer" I'd imagine it was serviced once before you got it. So it would be ok to have a flush done. The trannies, especially in our cars, are recommended to be serviced (pan drop, replace filter and fluid) every 30-50k. When they go 100k+ and then get a full flush, they see problems immediately after.

They are both 4T65-E transmissions in the GPs, the only difference is the GXPs get a couple hardened parts to handle the extra power of the V8 motor. Same problems tho if you don't maintain them.

It's the same transmission, with different gearing IIRC.

But no, I'd never flush a 4T65E transmission unless you bought the car brand new and did it every 40~K IMO.

GT (supercharged) and GXP have the exact same trans. Nothing is different, gearing is the same, parts are all the same.

GXP's have a aluminum block, its why they heat up faster. They are other reasons too, but thats the biggest.

yes i hate my block and so does my trans, damn heat transfer

gxp has tap shift though. so different valve body. still 2.93s and everything else is the same

Minimal details pfffffffffft.

I think another reason the GXP's heat up faster is lack of air flow under the car. The oil pan and how the motor sits in the bottom of the cradle has to have some affect on where the air can go around it. But thats for another day.

For those who say they are exactly the same.... sorry no. Wrong.

GM# 17804094 - TRANSAXLE, AUTO (SERVICE) (CODE 8CEB) - W 5.3C (LS4), 4-SPD AUTO TRANS (MN7), 2.93R (FR2)

GM# 17804095 - TRANSAXLE, AUTO (SERVICE) (CODE 8LBB) - W 3.8-2 (L26), 4-SPD AUTO TRANS (M15), 3.05R (F83)

RPO designation code is different, HD for one, Enhanced Electronics for the other. Gear ratio is different. While yes they are 4T65-E there are differences and some different internals. There are also other #'s and changes in the various year models, this is 08. But gear ratios and case codes change further.

Remember, Parts guy.

The supercharged model still has the 2.93's, L32 block.

They also get 3.29s too for the L32

GM# 24235529 - TRANSAXLE, AUTO (SERVICE) (CODE 5CBB) - WR 3.8-4 (L32), 4-SPD AUTO TRANS (MN7), 3.29R (FR9), MANUAL SHIFT AUTO TRANS (KB7)

GM# 24235527 - TRANSAXLE, AUTO (SERVICE) (CODE 5CAB) - W 3.8-4 (L32), 4-SPD AUTO TRANS (MN7),
2.93R (FR2), (EXC MANUAL SHIFT AUTO TRANS (KB7)

I said various other gear ratios and options in other year ranges.

3.29's was only in the comp g

True, but regardless, they are all plagued by the problems of a weak design and alot of abusive owners.

If you maintain it properly, just drop the pan, replace filter, and refill with 7-8qts of Dex6 AT Fluid every 40k(ish) you shouldn't have any problems.