Hey guys in the middle of swapping the old 5.0 motor for a rebuilt one and putting in a new transmission, now the motor and teams are already out of the truck at this point.....I went from the stock 15's to 20's with a 275/45/20....with having the motor and trans out is there a way to correct my speedometer or do I need to wait until the truck is back up and running?

 

There are gear calculators out there that will get you into the ballpark for your setup.

Here is one I've used before:

Speedometer Gear Calculator