I believe I have and injection pump problem on my '88 F350. Upon deceleration from highway speed, I've got a serious miss, rough running condition that occurs under light pedal. Idle is a little rough, but no problem under acceleration or full throttle. Return lines have been replaced, and I don't suspect air entrainment. I have run several tanks of donated Jet A through this thing over the past few years, but have rationed in quality 2 cycle oil and conditioner. I'm concerned my pump internals may be suspect. Ideas??