Try pulling the computer out and check for loose wires in connections. My car did this awhile ago and it took me awhile to trace that one down.
Have you tried swapping computers, it's rare that they go out, but mine did. Autozone has remans for $100.
306 with all bolt ons, letter cam, ported E7's, T5 swap, full exhaust, 3:55's, 2" drop, and the worst paint you'll ever see or feel.
Dyno'd 300/316, 2745lbs-track scale
Best ET………12.4@108, 1.66 60ft on 8" ET Drags.