Having problem with 1999 ZX2 with 60,000 miles. seems to be fine when cold, but after 25 minutes running seems to jerk and jump when starting from stop signs, etc. or creeping in expressway traffic. after another 20 minutes seems to get somewhat better, and then very intermittent. sometimes seems like it jumps between first and second gear, and then back again, related to power. a firm press on the accelarator from stop lessens the problem (or masks it). took it to my mechanic, and of course nothing happened during test drive. transmission shifted fine, and he seems to think basic transmission is ok after driving. although intermittent, something is definitely wrong. saw service bulletin regarding range sensor. would this have these symptoms? mechanic put on computer--no codes, and engine light has not come on. replaced spark plugs, transmission serviced about six months ago, fluid levels are ok. thought it might be bad gas, but have put in the best, and it does not seem to help for long. any ideas?