1999 chev tahoe 4dr

MY tahoe is misfiring on cylinders 2 and 7 according to the electronic
diagnostics. I've changed the spark plug wires, the spark plugs,
distibutor, fuel pump and fuel filter, still missing

I have had the same problem. Two things contributed , one was a broken tab for the screws that hold the distributor cap. The other and more confusing was a loose header to exaust conection. If this is the case you get a false reading at the O2 sensors and the computer gives more fuel to the engine causing the misfire and of course poor gas mileage. Hope this helps.