I have a 2006 silverado 5.3 Z71 crew cab. What can i expect to see my average fuel millage differ with the 87 tune? And is this guaranteed?

Thanks, Stoops

I have a 2006 silverado 5.3 Z71 crew cab. Is there an option to take the speed limiter off with your tuner? I see the TM stuff but not an option for a speed limiter.

Thanks in advance!

Stoopstroop