I have a 00 trailblazer that has a misfire in 3 and 4... I have already replaced distributor plugs and wires... Ithe still runs rough.. all the way up to abt 3000 rims then cleans up... I have a egr valve come that is new if that does not fix the problem I'm at a loss.. someone pls help me fix this

 

Start with a fuel pressure and leak down test. Do a search you will easily learn how to do this and it only takes a few minutes to do. Post your results.