1996 Toyota Corolla

A little frustrated and puzzled
March 2010- car had been running fine and just died
something happened that messed up the distributor
we had it replaced but there was still considerable missing/hiccuping when accelerating
had a local mechanic look at it but couldn't figure anything out
it did it more when car was cold
took it to Toyota dealership-they checked O2 sensor and quite a few other things: fuel injectors, put in original equip plugs and wires, replaced computer with another one(used) and some other stuff
it was running better but the missing/hiccuping was still there some
they felt it was something electrical but said it could take a while to trace it down
we had already spent several hundred on a car worth 1500 and didn't want to put more into it
we continued to drive
over the warmer months it got better to where it was almost nonexistent during the summer
now that it has gotten cooler it has started doing it a little more
gas mileage has not dropped over this period
we really don't want to spend any more money
any ideas on what is going on and do you think there are any concerns with continuing to drive it?