2004 GMC 6.0 4L80E & manual Transfer into 1978 Ford F-100...Trans????'s

Everything went in smooth, got the 4X4 low & Hi working...motor is plenty for off-roading, sand duning e.t.c
Finally got it on the freeway and that's when Problems started happening... The original HD truck came with 29" tall tires with 4.10 rear/front gears, the Ford F-100 has 32" tall tires with 3.50 gears...For some reason it won't stay in overdrive, it keeps downshifting to 3rd gear, sometimes into 2nd gear...If I manually shift thru the gears it shifts really good, but if I put it in drive and let it shift by itself, the tranny hesitates from 2nd to 3rd and to 4th. In the tune, I made changes in the speedo calculator that it has 3.50 gears and 32" tall tires but didn't fix the downshifting or hesitation...
A buddy of mine told me my problem is the Torque Converter apply and release speeds? Could it be? I have never adjusted the TCC at all....:unsure:
The transmission only has 47,000 original miles

Any help or guidance will be appreciated...

This may be a stupid question, but you said you adjusted the speedometer, but did you also adjust the shift speed tables? Those speeds will still be off since they were originally choosen based on the 29" tall tire and 4.10's.

in the speedo calculator you can go to a tab that says shift point correction make sure to hit apply the also

I've never used the shift point correction, Just tire height and rear end gear ratio....Opened up the tune set tire height and gear ratio back to stock, also added new tire height and gear ratio's, I hit the apply button and it pretty much changed everything that I needed....:cool:

Didn't work....Well i guess tranny is going to an expert!....:D

Hello Gameover,

Sorry to hear it didn't work out. Post (or send me) the tune if you want - sometimes a second pair of eyes picks up something initially overlooked.


Regards,
Taz

Ok here's the file, this is after the shift point correction that EFI Live does...

Hello Gameover,

Some of the part throttle downshift speeds were greater than their corresponding upshift speeds - this would make the shifts erratic at best. Give the attached tune a try - it uses stock 2002 LQ4 4L80 shift speeds - adjusted for 32 inch tires and 3.50 gears. No other changes were made to the tune.


Regards,
Taz

There's a spreadsheet on here for shift points you can map upshift and down shift as well as tcc lock and unlock .
I'm not home to post it but just search you should find it

We'll after 2 weeks of diagnosing and a semi-rebuild of tranny...I figured out what it was...