Old problem. It has done this since purchased in 1998. Sitting in driveway results in battery undervolt after a couple of days. Turns the engine, but temporary drop to less than 12.5 volts keeps the fuel pump (replaced) from generating enough pressure. Has anyone ever sourced the drain on these vehicles? 4.3 V6 Vortec, auto, 2 wheel drive, PW, PS, PB. totally unrelated comment...the fuse for the gas gauge is labelled "4WD" on the fuse compartment lid! I have the 2WD truck.