96 Tahoe Gearing

[khenry]

I picked up a 96 tahoe 4X4 with no motor, trans, wiring and no engine control module. I installed a 383 motor, 4L65E trans, MSD EFI and TCM. The RPO codes for the rear end are, GU6 3.42 ratio and G80 posi. Tire size is, 245/75R 16. My question is why in OD my RPM is 4000 at 40 MPH?

 

[bigfootchiro]

Is your trans shifting through all of the gears?

 

[khenry]

Yes trans shifting fine.

 

[bigfootchiro]

If your trans is shifting fine through all 4 gears, and you have 3.42 gears in the rear, even with the TC unlocked in 4th, you wouldn’t be anywhere near 4K. Is the tach reading 4K? Does it sound like it’s that far up there to you? I’d hook a scanner up and read RPMs. Maybe your tach isn’t reading properly.

 

[khenry]

Yes the Tach is reading 4K. The MSD TCM controller has a hand-held monitor connected so that you can monitor the transmission in real time and its reading 4k. It feels and sounds like its up there. Could it be the gearing in the new trans I had built?
Thanks for your help bigfoot.

 

[bigfootchiro]

What parts did you install during the rebuild? A specific rebuild kit that you bought? I highly doubt it’s the gearing in the trans

 

[HiHoeSilver]

What happens if you get up beyond that? Does it drop into 4th?

 

[bigfootchiro]

What are the shift points on the TCM? Sounds like it’s not allowing it to shift into 4th, or even 3rd for the matter

 

[khenry]

Trans was built by Finish line. It shifts into all gears. It actually shifts thru all gears rather quickly.

 

[HiHoeSilver]

There is no way that thing is in 4th when it's running 4k at 40 mph.