I bought a 83 c10 with a 5.3 from a 2001 suburban and a nv3500 transmission from a 2003 s10. The problem I’m having with it is it starts very rough unless you time it right. I turn the key to prime the fuel pump and wait about 3 seconds and tap the key quickly and it fires up like a dream. But say I just don’t time it right, it will turn over struggle to start fire up but the engine idle drops and I have to tap the gas and fight it to stay on. Once it’s on it drives great idle doesn’t Jump when the clutch is pushed in nothing abnormal.