P2135 when below 1/4 tank of gas. Makes no sense

What is your question?

I'm having the exact same issue and even the GMC dealership is having difficulties troubleshooting it. It seems to happen to me when I get below 80 miles to empty on gas which is weird. The dealership changed out the throttle body harness and thought they had it fixed filled up my tank for me and worked good till I got below a 1/4 tank of gas and what do you know the reduced engine power mode and P2135. Crazy stuff and driving me insane.

What makes this problem better or worse?

when below 1/4 tank of gas

How long has your 2005 GMC Sierra 1500 had this problem?

two months