Might be the pressure switch--pull the pan-- it is the tin looking part that is attached to the valve body.
If someone has a Tech II, and knows how to use it,-- they can check the operation.
If you want to guess -replace that. It is not very expensive.
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.