At speed the vehicle tries to stall or lose power?

Starts right up first try. Idles fine, smooth engine. No smoke. At speed the vehicle will want to stall or lose power. When it does this the service engine light comes on. It will start right up after this if it stalls. It has a new distributor, rebuilt starter motor, new fuel pressure regulator replaced, new fuel pump, new fuel filter, has a battery disconnect, new air filter. It's like it's starving for air or something. Shifts fine. Someone spent a good bit of money fixing many parts, but still has the problem.