I recently bought a 03 rcsb Silverado with the 4.8 and the last owner swapped it to a t56 trans, and I guess he never got around to fixing the speedo on the truck, I thought it was the cluster messed up but it wasn't. Anyone have any ideas to fix it?

 

Not sure the VSS is the same. Check to see if its plugged in at all. I think if it is you should get a speed - not the right speed. There may be a conversion box or simply a parameter in HPT to change.

 

vss is the same signal, teeth per mile maybe different though.

 

any tuner worth a damn can fix it. I did the same swap couple months ago in my truck, changed the VSS to the correct tooth count; like TrendSetter said.