1997 Chevrolet Venture starts knocking and cant go faster

I have a 1997 Chevy Venture. The van started knocking and would not gain speed. It was winding out the gears before shifting. Then a heater hose blew and I lost all antifreeze. Got the hose fixed and think that the oil pump is bad. But not sure about it now. The van started knocking and would not gain speed. It was winding out the gears before shifting. Then a heater hose blew and I lost all antifreeze. Got the hose fixed and think that the oil pump is bad. But not sure about it not gaining speed and winding the gears out. What could the problem be.