calibrating the speedo

[K5Greek]

i put 33" tires on my truck and now the speedo is off. how do i do this. isnt there something on the tranny that i change or is it done by computer chip.

 

[chevyk2500hd]

I think this link will help. It has been dicussed on the IFS section but I think you should have a DRAC/VSSB.
http://coloradok5.com/forums/showthread.php?t=162205&highlight=drac