1996 Ford Ranger

Hi, we have had multiple issues with this truck in the last couple of weeks(which is to be expected with the miles) The truck hesitates and has very low power output. When you stop and try to take off it barely moves. Once speed is up it seems to do ok. It seems to get worse with the hot weather. Within the last couple of weeks these items have been changes o2 sensors, coil pack, checked timing, clutch, slave cylinder, and checked other parts which were ok. There are no codes. The engine also seems to be running warm. My husband bought flush to flush the radiator this morning and on the bottle it said to turn on the heater for 10 minutes when he did that the truck started to run better. I was leaning more on the fuel pump side, but since this morning we were wondering if it was the radiator being clogged up. I can't afford to change parts that would do no good. Could the radiator making the engine run warm cause it to have low power and hesitate? We are at our wits end!