Help! 94 4.3 Running Aweful!

I have a 94 caprice with the 4.3. Lately the car has been hard to start and roughly It boggs down, smells of fumes, and sometimes stalls out or starts to run fine. Any ideas? Also i have no check enigne lights.
Also the car backfires through the intake as if its mis fire'n then after about 5 mins of driving it runs fine for the rest of the day

Clogged fuel filter, low pump pressure, clogged/restricted fuel line, fuel pump, evap canister, pressure regulator etc. I'd check all of that - line pressure should be 55psi minimum at the rails. There should be a Schrader valve on one of the rails that you can attach a fuel pressure gauge to.

The car also is back fireing through the intake. After driving for about 5mins it runs fine! Please help!