1989 Dakota Surges Code 55

This thing is baffling me. It flashes code 55. Supposedly something to do with computer. I checked siring to the unit, unplugged and replugged harness. Reset computer and replaced EGR vacuum lines. Seems to have quit surging but still stores code.
Any suggestions?

Thanks

code 55 is an "End of Code" message; in other words, it's ok, no codes are stored.

I recently got code 42 auto shutdown relay, and 51 lean condition in fuel. I replaced relay and still has the problem. Steady throttle at about 2000 rpms and it stumbles.
Any suggestions?