88 S10 surges at normal speed
 

I fixed one problem and now I have another. My 88 S10 Blazer surges when you get up to normal speed with only light pressure on the pedal. I thought it was the shift cable on the tranny so I adjusted that. It improved the shift but still surges. It seems to want to downshift/upshift. It is annoying the bejeezus out of me! If I pull the tranny down into D it stops but then it revs too high on the expressway and uses too much fuel. Any thoughts?

I am a Newb But it sounds Like a Vacuum issue to me.

Other Things to Check:

Check inside The plenum for leaking Fuel pressure regulator , Fuel Hoses, Injector Nozzels, a small leak may do Just That.
Check Vacuum, EGR Valve, and Computer Codes for a bad sensor maybe.
dont overlook The PVC Valve either.