I'm guessing this is all from looking at the factory "tach"?

Those fail by reading high. ALL OF THEM. I have one that reads 3 times the actual RPMs, and others report failures even higher than that. Hit the Electronics forum on this site for many discussions.

I'd suggest starting out by comparing the "tach" (wavy pointer "sporty" trim package thing in the dash that isn't really an "instrument") against some sort of known accurate test equipment.

Most likely, your TPI is doing what it does best: protecting your motor from ever seeing any kind of RPM-related stress.

Odds are however, you'll need some form of speedo recalibration as a result of changing the rear gears. I'm going to go out on another limb and make another wild-a$$ guess: you went from 2.73 to 3.23 gears, no?

 

So as a rough guess, I'd say you should be around 2000 to 2200 rpms in overdrive, while at 70 mph. That's literally less than HALF of redline. You should easily be able to tell just by feel if you're safely chugging away at an actual 2100 rpms or if the engine is actually at redline. My tach in my 89 reads WAY off. About 2500 off. Now I have my Holley EFI which reads right off the ECU, so I KNOW it's right.....but when I'm at full throttle, the engine screams right past the 5000 on the factory tach on it's way to high 7000s. ...but I know it's off. ....when you ARE actually coming up on redline, the engine shouldn't be reving overly quick. You should just be able to feel it. Sure, you keep you foot in it and you'll blow it up, but I don't know anyone who actually shifts off the tach. Many manual cars don't even HAVE tachs, and drag racers use shift lights because you can't drive and watch the tach at the same time.

....so is it really reving that high, or is it just the tach?

 

 

What did the test eqpt say the revs REALLY are? Like: dash says xxx; test eqpt says yyy?

 

Yeah, I'm with Sofa at this point....really need to know FOR SURE what the engine is doing. ....and if it IS revving high....like you say, then I don't see how it's NOT the transmission. You said they hooked up the transmission at the tranny shop? Can they test the clutch packs without a test drive? Sounds like maybe a slipping or going bad 3-4 clutch pack? I'm no auto trans expert though....

 

Hookup a scan tool and compare the ALDL engine rpm with the tach.

GD