98 k1500 5.7 vortec. I have a new jasper engine in my truck a few months ago. I know have a rough idle I get a P0300 and get bad gas mileage, the exhaust smells of gas/rich. I put a new fuel filter, distributor, plugs, cap, rotor, wires, air filter, cam senspr, tps, crank sensor, ecm. I don't know whats next. I have had trouble with it starting the old and new engine even before I put the engine in the truck. It starts cold but when warm it cranks a lot before it fires up. I was thinking fuel pump?

 

I heard bad fuel pressure will give u a rough idle, a random misfire and hard to start?