Turned out to be a bad fuel pressure regulator. And I JUST fixed this a few days ago. Problem's been going on for a long time. It would drive fine off the line but it was VERY noticeable when going into heavy boost from part throttle/ cruising. I realized that it had nothing to do with the trans since I got a trans swap done like 3-4 months ago & even with that newer trans, the same symptoms persisted. Rented a fuel pressure tester from AutoZone & KEY ON was fine. It was about 48 PSI. However at idle, it would dip down to 40 PSI which is no good. Bought a Sorensen brand one from AutoZone for $35. Everything works better now. Around 50 PSI at idle. That Actron tester is a piece of sh1t with inconsistent readings but you get the idea. FINALLY able to get my GTP to act normally when trying to get into the high RPM range from a cruising speed. The RPMs now smoothly & gradually rise instead of shooting up midway through. Guessing the A/F mixture was severely leaning out with the clogged FPR. Funny thing is that I never noticed any fuel in the vacuum line attached to it but I read that the diaphragm can rupture OR - in some cases, probably like mine, clog up & just end up sitting there and doing nothing.
