The truck has a brand new 350 vortec motor in it and at the first gear going to second will skip then backfire but as soon as you give it a little more gas, it will run right but the idle speeds it will skip and backfire. The truck has new plugs wires and coil pack that's why I ask what's wrong because I don't have a clue. Also when you put it in first gear or any other gear it will not hold a constant rpm around 2000 or 2500 without cutting up and backfire. The truck is automatic transmission. Please help thanks.

 

you have any engine lights on? check fuel pressure