98coppermetallic

Hey guys, I have a 98 Silverado or K1500. I had a problem with a p0300, p0303 for years. I had no power up hills and hard to start. I just put a new jasper long block engine in the truck a week ago hoping to solve the problem. I am still getting a p0300 and cranks a while before starting. I put a new engine, waterpump, plugs, wires, cap, rotor, dist gear, air filter, fuel filter, egr valve, cam sensor, crank sensor, tps at the cost of $4500.00 where do I go now??? It's driving me nutts!!! computer problem? Fuel rail? Any input would be greatly appreciated.