1992 Nissan Sentra engine lurches at low throttle in overdr

Have been "shade tree" mechanic on trucks-cars & motorcycles many years yet am about stumped. On '92 Nissan GA16DE replaced injectors, fuel filter, checked connectors, R&R vacuum hoses, R&R plugs & wires, new MAF, cleaned distributor & cap & rpld rotor, can of SeaFoam thru booster vacuum hose, cleaned throttle body, injectr cleaner in tank, premium fuel in tank, no trouble codes in ECU- engine always starts & is reliable yet begins to lurch at even throttle cruising speed after shift to overdrive or high gear if overdrive is turned off. Gets worse/better some times but can not be attributed to weather/moisture. Suspect distributor. Thanks