Should not make that big of a differance.
If you are using just regular pulleys then the only way the timing would change is if the belt was old and stretched or if the head was shaved.

Might be that the computer just has to relearn all of its specs. The CVH that came in the Sierras has to do this for so many miles (or hours) before it runs correctly.

I am currently playing with a completely shaved SOHC motor.


TF