1994 Chevy Silverado Loses engine power while driving

It is a 4x4 5.7L with a throttle body system, While at freeway speeds it more noticeable, If im holding it right at 70mph for example without moving the pedal it will lose power slowly, it will drop about five MPH then all the sudden power will come back and speed up. Also when im at a complete stop and give it alot of gas it just feels like there is a little four cylinder under the hood. Then all the sudden the V8 will come back and off I go. Some new or recently in the last year I have replaced.

Fuel pump
plugs, wires, cap and rotor
alternator
fuel filter, air filter (this past week) along with oil
I have taken off the muffler cause it was leaking and replaced it with a pipe, I think the catalitic converter is bad causr it rattles inside. I have cleaned the throttle body well, and I was told to take off that canister that hold all that carbon build up and blow it out. Well that didnt work so well. The hole was plugged and it exploded in my hands. Does anyone have and suggestions? I dont have alot of money and need to do this myself. Thanks