I have a 89 s10 blazer 4.3 when idiling does well then when stomp throttle its bogs but picks back up. Other day was driving going up hill gave throttle and it down shifted but didn't gain power any ideas. New tps, map sensor, egr valve solenoid, ignition coil, coolant temp sensor, fuel filter, pcv, vacuum hoses, battery.

 

Possibly the fuel pump.

 

I know that the 4.3 in my S10 will bog down like you said when I stomp the throttle but only when it is cold. Have you noticed it running cool? If not it's a possibility that your spark plugs are fouled out and not burning as hot.