I have a 95 GMC G3500 5.7l, with 200K+ miles. It was running rough and I had some knocking at accel, so did a major tune up, now it runs strong but idles rough in gear only. Changed EGR valve but still rough. Any ideas?

 

I had to replace injectors, ignition modules, both knock sensors, and I'm still getting codes. Just the spark plugs are ridiculously expensive.