Fuel guage problem

2008 Chev Silverado 1500 LT 5.3 V8 6.5 ft box extended cab

The fuel gauge on my truck stopped working and would have needle go all the way to E and Fuel range show ---. Clearing codes would allow the fuel range display to work and low fuel light come on for a 10 seconds to a minute or so and then it would shut off again. If I continually clear the codes it eventually creeps up to the proper setting and the distance to empty reading shows correct number ... until it dies again. This is accompanied often by a overvoltage message (I cannot remember the code).

To be able to use the truck I would put $20 of fuel in every 2nd day and drive approximately $20 worth of distance. If I just put fuel in I knew I was OK. One day when taking a longer trip I put $50 in. The gauge started working again and worked until approx. 1/4 tank at which time it started the Fuel Range --- and needle on E game again. Anytime I have 1/2 tank or more the gauge works.

Local mechanic suggested is a fuel gauge in the tank (sender unit?) and would take 3.5 hours to replace. The fuel pump was replaced April 2015 and I believe the sender is part of fuel pump? Any comments on this?

Just one of several annoying issues as this truck ages ....

Mike