So the dealership near my house is Henry Brown GMC. I went there today because my Parking assist off warning comes on every time I start the truck. Also the trailer brake soon. I adjusted the tire size in efi live, And ever since this has been happening. The dealer said I would have to pay a diagnostic fee because it's lifted. I felt ridiculous. The truck has 4,000 miles on it! What do I do....?

Ignore the lights - or pay to play......... Neither a good option.........

I hear ya, my is tottaly stock and the darn parking assist light sometime warning goes off from time to time also. Might be something going on here

Try Cardial (formerally Martin) GMC in North Scottsdale. Ask for nick. Cool guy, no B.S. but you might want to take out your EFI. They don't care about lifts, but not real friendly with programmers.

You can also try Midway. I have heard that they are cool with just about anything.

Moved to Warranty section!

So the dealership near my house is Henry Brown GMC. I went there today because my Parking assist off warning comes on every time I start the truck. Also the trailer brake soon. I adjusted the tire size in efi live, And ever since this has been happening. The dealer said I would have to pay a diagnostic fee because it's lifted. I felt ridiculous. The truck has 4,000 miles on it! What do I do....?

Do you have a stinger, in the hitch?...If so that will make it go,the park sensors see that.

My rapid hitch will cause the problem with the back up warning. Also, if your parking brake is on the back-up warning will be displayed in your DIC and will stay there for about a second after you take the brake off.