Truck revs up but doesnt accelerate like it should. What could be the cause

What is your question?

So my truck a 1993 Chevy k1500 4x4 manual 350 and what it's doing is that when I'm driving down the road and I want to excelerate it revs up but doesn't go any faster but after a couple of seconds it starts to slowly excelerate. It's also the same when I start in a dead stop I release the couch and it starts to move like normal but I try to excelerate more and it revs and takes a few moments to start to excelerate.