Just picked up a 2011 Chev. Silverado Z71.  Has a rebuilt title.  Unit drives nice but fuel gauge sits on completely full or empty.  Neither indication is correct and the computer that calculates distance left on tank is totally messed up.  I suspect something either didn't get hooked up correctly or a sender is bad.  Can anybody tell me how to diagnose this problem?  Thanks so much!  When I picked it up in Wichita, KS to drive home, I noticed that gauge was setting on full.  I thought "how nice of them to give me a full tank"!  Just about ran it out of gas and it started hiccupping and stalling.  Was able to make it to a gas pump!  This unit has a 5.3 flex fuel engine.