hen setting still the engine idles smooth but when i put it in gear an take off the engine runs real ruff.
idles ok when not in gear but runs ruff when in gear on 1990 GMC Suburban 1500
Could be many things, state of tune, good spark plugs, needs good ignition system. could be a vacuum leak check intake track ducting for cracks or loose hoses or clamps. To hard to guess at without being able to experience the problem first hand or do basic diagnostic tests.