91 Camaro RS 3.1L will run rought sometimes

:confused: We just bought a 91 Camaro RS 3.1L V6. We had it 2 day and the trouble started. It would start running rought and lose power when driving.

We started with the fuel pump and filter, fuel pressure reg. Replaced the battery. Clean the injectors and the fuel rail. The fuel pressure at the fuel rail is 40 psi and does not fall off. We replaced plugs, plugs wires, rebuild the distributor, and replace the coil. The EGR value, the throttle sensor. Then we replaced the ECM. Still no joy. We drove it for 10 min to let the ECM relearn. We still sometime it will run great and sometime it runs so rought you can't drive it.

Any help on what to try next?

When you rebuilt the distributor what exactly did you replace?

We replaced with a new one and new cap, rotor, wires and plugs.

Have the ignition module tested, several times, if bad, replace with a AC/Delco unit only as if you use a aftermarket, you'll be right back in the same boat in no time.

We found the time belt jump some teeth. It running better but now we have no power it sound looks like it is sucking too much air.
Any new thoughts?