??? Ok getting the P0300 multilpe misfire code on my 2001 GMC Sierra with the 5. 3L engine. Got new plugs and wires. Checked spark with spark tester all coils are firing. Check resistance on injectors they checked out good. Tested fuel pressure key on 52, engine running (idle) 48, leak test for 5 mintues no drop in pressure. Vehicle is running rough, hard to accelerate, stumble during acceleration. Dual exhaust on this truck driver side exhaust is just barely blowing out passenger side blowing out good. Was getting code before I notice exhaust pressure. Could it be Cat Converter and fuel pump?