Low Power with excessive fuel consumption

My 91 chevy 4wd, 350cu pickup becan showing loss of power during acceleration this week. The strange thing is the amount of fuel that it is consuming. It burned through a half tank of gas just driving 70 miles. The carburator sounded like it would open fully to get any acceleration at all. When acceleration up a slight incline the pedal is floored and the truck moves about 10 miles an hour. The transmission shifts normal and the transmission fluid smells normal. When my truck is in park is revs up normal. I'm confused.

I would check for a plugged converter loosen the bolts in front of it and move the flange about 1/2 inch apart. If it runs good at this time buy a new one and tune up the engine.