I just had a problem with flexplate bolts backing off constantly, so I eventually and recently installed an SFI heavy duty flexplate with new bolts. Before I installed the new plate though I noticed the 1-2 shift was around 45 mph, where it use to be around 55 mph when the transmission was brand new from the dealer 4 years ago. After installing the new plate I hoped by some miracle that the early shifting would go away with fixing the flexplate, but knew it wouldn't, and it didn't. So can my transmission really be dying after 4 years of average use? I have not raced it, but have driven it spiritedly like anyone else.

The RPMs seem fine when driving normally, but at WOT the 1-2 shift is at 45-ish mph, and 2-3 is at 90-ish mph (use to be 95).

 

Shift points are not controlled by or inside the trans but by the PCM if your shift points have dropped something has changed electrically with the car. TPS would be a likley suspect.

 

You have no idea how good that is to know that. But could a slipping transmission cause different shift points? I will hook my scanner up to it tomorrow and read what it says about the TPS and other info. What should the TPS be at while idling, and WOT?

 

No sure about the tps reading. But as for the slipping changoing shift points if anything that would make them later.
Have you changed tire size. rear end latley ?

 

No, the tires have been on there for 3 years, rear end has been the same and fluid changed 2 years ago. When I took the old flexplate off everything seemed fine, no leaks, no trans fluid anywhere, no excessive oil around the engine/trans/crank. And the shifting being later makes sense, I just didn't think about it. When my first transmission went out it would hold at 6k RPM for a slight second, then make a violent shift in to 2nd. Eventually 2nd was completely gone as the band snapped IIRC. But now it still shifts smoothly/firmly in to 2nd without hessitation, when it hits 6k it shifts almost on the dot. It feels as it should. I will check out the TPS, and other things like MAF, codes, etc.

 

The trans was half a quart low, and it shifts noticeably firmer under normal driving conditions now. However, still shifts at 45 WOT. Did not get a chance to hook up a scanner and will do that tonight to see what kind of sensors/readings are going on with the PCM/engine.

I had a thought, though, with the flexplate being loose and causing a lot of knocking the knock sensor could be retarding the timing, and could that cause a loss of power like I'm seeing? I will see what the scanner says about the knock but don't know if it could cause such a drop. The trans has about 25k miles on it and was brand new when put in (not rebuilt).