88-s10 rough engine

I had reman engine installed. Have replaced: motor mounts; EGR Valve (2 times); Coolant Temp Sensor; Injectors; O2 Sensor: MAP sensor; Idle Air Control: rotor & Cap (2 times - rotor extremely pitted after 7K miles); plugs & wires (2 times); TPS reads linear on digital and analog meters; vacuum control module; used alldatadiy to test ESC and knock sensor -- tested good; vacuum is rock steady at 18 inches; harmonic balancer is good; Timing at factory spec; advanced timing (using Craftsman light with dial -- up to 35 deg adv. and no change in engine (very strange); all cylinders firing (timing light verification). Engine starts okay, runs moderately good until warm and then is extremely rough -- as if timing is swaping cylinders - major hesitation off idle. At 2000 rpm, smooths out.:banghead: