1996 Chevrolet Silverado Will crank but not start

Have replaced battery, fuel filter, fuel pump relay. Took to mechanic who kept it a week because it started sometimes and did not sometimes. He replaced air filter, cap and rotor, plugs and wires, crank sensor and hall effect sensor. He also checked fuel pressure which was good and hooked up to a different computer. So, $466 later truck will crank and has spark and fuel but still will not start even though it sounds like it is going to. When this first started we could jump it off and get it to start but not now.