Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Try starting it with WD40 or starting fluid. If it starts and runs for a bit, the main injection pump is not getting fuel feed from the lift pump on the rail - any of the circuit components, from a fuse to a bad pump could be faulty.
I can provide you with diagrams and guidance through the electrical checks. You'd need a multimeter and the ability and skills to use it. Please let me know how you wish to proceed.
If it didn't start on starting fluid, then the issue might be mechanical. A compression check on all cylinders would be the next step - normal compression should be in the 380-400 psi range.
The lift pump provides prime, so that sounds like we're back to my first response. Have you gone back to the shop and told them what's going on? If so, what did they say?
That would be my guess at this point - as I stated before, you would need to perform some tests which results would confirm the pump being bad.