[DirtyLarry]

You can always have any GM dealer reprogram the tire size with their Tech 2 scan tool. All they need to do is change the rolling diameter of the tires in the ECM. It is a couple minute job that that dealers usually only charge $20 to do. It helps them if you look up the rolling diameter of your tires a head of time before walking into the service department so they don’t have to look it up for you (and charge more for doing so).

A 4.3L in a full-size with larger than stock tires are not a ball of fire. Not much you can do but regear or swap in a V8.