I have a 2002 envoy with 172,000 miles that I bought about 6 months ago. everything was fine until it started to have a miss. Showed P0300. I changed all 6 coils and plugs. Still have P0300 Miss got worse , did a compression test, all tested between 174-185, sprayed starter fluid around base of intake manifold,no change in engine. Pulled upstream O2 sensor,no change. Pulled each coil connector while running and #1 and #4 seem to be the culprits. Swapped coils around and still #1 and #4 Should I now pull injectors and replace or clean them? Any advice or help would be very much appreciated.