I'm looking for a GOOD Auto shop with a mechanic that's very good at diagnosing code P0300 on a 2003 GMC 5.3. It ran very good, but sat a lot, the fuel pump went out and I replaced it, then it started throwing the code, I replaced the coil packs, wires, spark plugs, and it didn't help, plus it started smoking . I'm looking for someone that's very familiar with these engines and has a very good scanner that might narrow down the problem, I'm tired of just throwing parts at the problem.