I have 1994 Z28 with LT1 and the A4 automatic, what kind of RPMs should I be seeing @75MPH with 3.73 gears? I'm now seeing 3000RPM . The car seems to be screaming now, like it used to @90+MPH.

 

^that sound like a 4.10 rpm man..

 

My handy calculator shows, in O/D with a stock tire diameter, at 75mph:

3.73 - 2,550rpm

4.10 - 2,800rpm

 

what would the RPMs be if the tranny was still in 3rd gear @75MPH and not in OD? Would that explain the High RPM's? last shif point seems to be about 50MPH

 

That sounds right. My 700R4 equipped Trans Am had factory 3.73's and I put 138,000 miles on them like that. 70 MPH was indeed a hair under 2600 RPM.

The 700R4 has the same gear ratio as the 4L60E.

If you are seeing 3000 RPM, then you are probably not locking up the torque converter or getting it into overdrive.

 

Ok so I used the Tuner Cat program today to fix the speedometer, which it did, changed the fuel cutoff speed up as well, but now the engine is revving a lot higher. Didn't knowingly change anything else, is there something that I should change that would fix the OD not kicking in? This is turning into an adventure.

 

Do u take notice to see if it shifted into overdrive?

 

I think it did, but really screamed when I stood on it, almost like it went into 2nd @ 70MPH! The shifts weren't exactly crisp or hard, it was wet out when I was test driving it today so Iwasn't able to really push it. Just doesn't seem right. Really wondering if I screwed something up when I fixed the speedo.