97' vortec 454 engine & tranny swap questions

[efontenot73]

I have 85' K5 that I recently swapped in an 97' vortec 454 & 4L80E, 208 transfer case & painless wiring harness. Here's the issues:
Tranny shifting way late & hard, my computer showed speed of 14 mph when actually going like 45mph..... Any ideas? Motor & trans only has 34K so should still be good

Other mods include, cross-over steering, 12" springs in front. 8" springs inrear, and flipped hangers, tires are 38.5x14.5x16.5 and when going 0-30 mph hops like nobodys business...Any solutions?

 

[mnstrburbon]

Sounds like the CPU needs a tune for the proper tire and gear ratio of the current set up, not the original donor truck info.

 

[Avery4jc]

I think mnstrburbon hit the nail on the head...


http://www.pacificfab.net/
Give Pacific Fab a call... they are known for their 5.3 and 6.0 Vortec swaps but I'm sure they could point you in the right direction with your 7.4 swap.
In the meantime how about some pics! Sounds like a great build... I've often thought about how cool it'd be to put the drivetrain from my k3500 into my k10.

 

[Kenny78]

Does your 208 have an electronic speedo? If not, how are you telling the trans how fast your going?

 

[pennsylvaniaboy]

also another place to look is jim's performance. if it were my motor and trans i would go to jim's and get all the crap deleted and taken off. then get a stand alone for the trans.

 

[efontenot73]

I will look into getting the cpu reprogrammed, and pictures should be up tonight

 

[Avery4jc]

It's tonight... where's the pics?

 

[mnstrburbon]

And tow today, where are the pic's.

I also dont know much about the vss but i read there are 2 different ones maybe you need to swap it out with the og one.