4T65E-HD Slip on light throttle downshift
So I have a pretty uncommon car, a 1998 Oldsmobile LSS with the 3800 Supercharged and 4T65E-HD. I'm trying to figure out what is going on with the transmission, it has some random slipping. I first noticed the slipping going up a very steep hill one day, noticed the engine was revving but I wasn't pulling the hill as well as it should. The slip isn't bad, but if I take off about half throttle sometimes it will slip, the car will move forward slowly, the engine will rev to about 3000 then catch and drop back down and take off perfectly. For some reason it does this more frequently on right hand, slightly sloped turns. No slips full throttle, and all gears shift crisp. However, on light throttle when the transmission downshifts from 4th to 3rd, it will slip for a second and then jerk slightly and catch 3rd. However its only at light-medium throttle, full throttle downshifts are crisp and firm.
I've added the TransGo 1-2 and 2-3 accumulator springs/spacers, and a decently sized stacked plate trans cooler, did a pan drop/fill twice using a WIX transmission filter, and tried Castrol Dex/Merc and Valvoline MaxLife high mileage Dex/Merc and there has been no change. Any ideas? Thanks!