Chrysler Repair: driving hesitations, spark plug wires, chrysler lebaron

Question
I am having a little trouble while driving my 1991 Chrysler lebaron. It is a 6 cyl. automatic transmission. When driving, it seams to hesitate or slightly jump (like pumping the gas a little, or running out of gas) it does this from around 30 mph to 65 mph. I replaced the transmission twice, the first time it was jumping, the second time, it would drop into second gear and stay there until i restarted the vehicle. the only codes are 12, 17, and 55. I have replaced the thermostat. I've put in a new fuel tank, pump, fuel filter,fuel injectors, and plenum gaskets. The slight irregular jerking is very annoying. could this be a sensor causing the slight jerking? The car doesn't seem to be missing (in time). could it possibly be a leaking manifold gasket? any insight would be greatly appreciated.

Answer
Hi William,
Have you check all the vacuum hoses for possible cracks or disconnections? How about the PCV valve, have you changed that?
How do the plugs look? Is one cylinder's plug fouled? Have you done a compression check lately? Have you checked the spark timing? Have you looked under the hood on a dark humid night to see if you see any arcing from the spark plug wires. How are the cap and rotor?
Other than that, you may just have to keep waiting for a fault code to appear.
Roland