1994 Chevrolet S-10 stalling on acceleration.

Truck runs great sometimes, then runs very bad. When running bad, in park, and stepping on gas, sounds like tbi is fluttering. When I take off, truck will not gain speed, sounds like it is falling on its face.I have changed 02, canister solenoid, IPS, Timing chain, EGR, injectors, also dipped and rebuilt TBI, to include replacing accelerator pump in TBI.I have also set timing, replaced alternator, starter, water pump, fuel filter, two of the three relays on fire wall. Air filter, MAP, TPS, cap, rotor, wires, and plugs. Still runs bad, then good. Have found that sometimes I can feather the gas, or push it down slow, and it will take off. When I step into it, sounds like trans is slipping, and motor is stalling.I have spent all my money, and still no resolve. Help me please!