06 gmc 2500hd 4x4 6.0 gas

[Kevstr2]

I purchased the new i3 diablo sport tuner.
I updated the unit, then installed the 87octane tune. Seems to be running well. But everytime I go in and adjust my tire size using either the size in inches or in the tire size 275/70/18 to fix my speedo the truck goes crazy... Im backing out of the driveway and the speedo climbs all the way to 120mph then truck wont throttle up at all.
If I put the factory tune back its fine. If I put the 87 octane tune back on with no tire modification, truck runs fine. Install 87 octane with tire modification, truck goes crazy again!! Can someone help me fix this? What am I doing wrong?
thanks

[mikel]

load tune with no changes, post the backup and last tune written files from the i3 drive/tunes fodler here and confirm what the new tire size is.

Thanks