2001 silverado 2500hd 6.0 4x4 wheel size issues

[Tsegreti]

So I tried entering wheel size after the speedometer was half speed from changing my axle ratio. Only problem is it won't save and when it say saved it makes the vehicle throttle on and off kind of bucking. Please help. Also any input on parameters to modify for plowing.

[Diablosilverado]

I'm having the identical issue right now on my 2007 classic 1500. Shows half the exact speed on speedo. This is when I install an easy tune and change the gear ratio to 3.73 from the stock 3.23.. I manipulated the tune and told it the truck has 2.00 gear ratio and now it's still 8mph off at actual 75 mph. If I try to modify the tune, it will not allow me to save tire size and when I flash the ecm, it wont accelerate at all and the speedo jumps from 0 to 100 and so on. I believe the ecm thinks the tire size is 0.0 so it thinks I'm doing a million miles per hour when I try to accelerate

[mikel]

Load the tunes with no changes for tire size then post the backup and last tune written files from the tunes folder here and tell me what the new tires are please.