I've driven about 500 miles since getting my 2000 GTP, after having it completely serviced by the local GM dealer, to include a complete transmission flush and new filter. The car shifts perfectly under normal driving conditions and in normal shift mode, but part of my commute is through DC traffic and at partial trottle. Under some conditions the transmission is very slow in shifting between 1st and 2nd, and 2nd and 3rd. Using Performance Shift mode eliminates this but I'm not sure if using Performance Mode in commute traffic is OK. I've researched some alternatives:
a) Reprogramming the computer to alter shift points. This approach always seems to requires the use of Premium fuel which is not an option.
b) Installing a shift kit like the one offered by 3800performance.com, the Thrasher 4T65E Shift Kit which uses a dual spring setup and precision height shims which are placed inside the 1-2 and the 2-3 accumulators.
Are any of you familiar with what I describe or has anyone installed such a kit in their GTP transmission. If so, what changes have you seen in both normal and Performance shift modes?

Leaving perf shift on is not detrimental in traffic. As a matter of fact Pontiac did away with the option and reprogrammed the PCM to be in "perf shift" 100% of the time.

A word of caution, don't ever flush the transmission on a car that old again. If it had never been flushed before, all the flush did was jar loose all the debris that's built up in the tranny and made it more prone to failure.

I hope that slowness between shifting isn't the first signs of transmission failure.

But as for your question, Herc's got a point. Performance shift really only kicks in completely when you're gunning it. Inching in traffic is nothing in PS.

x2 on the tranny flush....if you buy an older grand prix never flush because of what arcxnus said....only drain and fill!!

You have a GTP, use premium fuel at all times regardless of whether you are using the perf shift or not! It's required by the car. By not using premium you are risking damage to the engine.

Anyhow, as to the tranny and perf shift. Doesn't matter whether you run it all the time or not. I used to have mine set to use it 24/7 before I got rid of it.

Also, performance shift has nothing to do with the requirement to use premium fuel, the reason is because of the supercharger.

Wow, I didn't catch that.

For the love of all that is holy, put premium in that poor thing before you chip a piston.

It's not an 'option', it's a requirement. If you were worried about gas prices, you should NOT have bought a GTP to begin with.

Premium is only 2 dollars more a tank.

And I totally missed it the first time but if you want to expect longevity out of that car by all means use at least 91 octane. Any lower and your car will start to knock. The PCM will pick it up long before you hear it and will pull timimg to prevent the motor from knocking. If the knock gets too bad you will chip a piston necessataing a rebuild. What you think your saving at the pump each fuel up is offset by the extra fuel stops you'll have to make because your not operating the motor in it's optimal mpg state.

you could throw a shift kit in it.

and yes, please put premium in it

the shift kit is cheaper at the W-body store thats what im going with this summer.....http://www.wbodystore.com/grandprix/w-body-store-shift-kit-p-56.html

Well, this forum has proven more beneficial than anticipated. Thanks to you all for the input, especially on the premium fuel. I didn't catch that in the owner's manual. I'll be on the lookout for tranny problems getting worse over time and keep you posted on the results.

Glad we could be of help don't be a stranger now.

stay aboard and start modding....and ease into the premium fuel just switching fuel fast can also mess with the engine/comp.

just go straight to 93. you dont need to be running that crappy fuel in there anymore

Don't worry about jumping right in. Only thing is the PCM takes a little time to adjust to the new octane.

I had 5 gal of 87 left and filled up with 93 today. On that, my car says low fuel with 5 gal left in the tank. Is there a way to correct that without spending a fortune? My 2002 GT had about 2 gal on reserve and had a very accurate guage. This one, not so much.