I have been having some trouble with my 99 GMC serria. The code scanner says the number seven cylinder is misfiring. I have changed the plug and wire and the coil is firing. A guy at the auto parts store said that his did the same thing and that it was "trash in the fuel injection system." So I changed the fuel filter and add some red line fuel injector cleaner. I am still having the problem.

The truck seems to run fine at highway speed, but ideals like crap and lunges back and forth when stopping.
I am going to try and pull the injector and clean it.

Has anyone ever seen this problem before? Am I on the right track? Any help will be greatly appreciated

 

I've been through the same thing, the injectors are disk style and the trash is easy to clean if you take the injectors off, its actually really easy on these trucks, a few bolts and undoing a couple of fuel lines and the rail and injectors are off. I cleaned mine with some GM spray but i think carb cleaner will work well as well. Hooked it all back up, changed the fuel filter again and no more problems. Just be careful not to break any o-rings and to clean the fuel rails as well. I had gotten a bad tank of gas at a station that was recognized on the local news for selling bad gas.

 

Did you fix this problem? I have the exact same thing happening except they're new injectors.