1996 Pontiac Grand Am Missing

I have a 1996 Pontiac Grand Am, with about 220,000 miles on it. Recently it has started missing while driving usually around 1,500 to 2,500. The check engine light has stayed on, flashing every once in a while, with the door locks locking and unlocking randomly. It also seems as though sometimes while driving it does not want to change gears, for example while driving at 35mph the rpm is at 3,000. I am pretty good with working on it, but cannot seem to figure this one out. I even took it to a mechanic, which produced the same results both times. I have changed all vac lines, spark plugs, and spark plug wires. I need help, no one can seem to figure this one out. Your help is greatly appreciated.