Hiccup while accelerating

Engine is a 350 TBI. When I attempt to accelerate the engine "hiccups", the RPM's drop, the vehicle jerks forward, and sometimes a light backfire is heard. Basically the more gas needed the more frequent and stronger the hiccups become (hills are the worse).

I have replaced the following since this has started:

Fuel filter.
Spark plugs.
Distributor cap.
Distributor rotor.
MAP sensor.
Ignition control module.
IAC (cleaned not replaced).
Engine coolant temp sensor.

I tested the PCV and found no leaks

Besides making the truck more responsive it did nothing for the actual hiccups. This only happens under load, If I rev the engine while in park it is smooth and sound strong no knocks or bangs. While driving at a constant speed there is no problems (does not matter the speed, only getting to the speed).

Other details:
No check engine light showing and no codes either.
Previous owner removed the catalytic converter.
Attempted to see if there was a change in idle with the O2 sensor unplugged but no change.
Strong smell of raw fuel coming from exhaust.
Tested each spark plug and all were strong.