Some stalling and surging on a 1995 Olds Cutlass Supreme

My cutlass supreme was acting up with intermittent stalling at stop signs and stoplights and also surging especially on the highway. There are no check engine lights and nothing comes up on the scans. We have replaced all of the worn parts and checked out the sensors, replaced the ones that are bad. So far we have done plugs, wires, fuel system including filter, fuel pump, fuel pressure regulator, pcv valve, iac valve, throttle position sensor, oxygen sensor, battery, etc. We have checked and tested other sensors such as the crankshaft and cam sensors and they have tested fine. We have also done a fuel treatment, while a lot of the problem has improved since we replaced the tps sensor and battery last night there is still a stumble and I am wondering what we can do to follow up. Do we still need to check the egr valve and the ecm? Would these items cause this problem or could this be a re-learn procedure we need to complete? Any ideas? The mechanics and the garages I took it to are a little stumped, not sure where to go from here