Transmission or Clutch plate

When im in 1rst, 2nd, or 3rd gears (only on initial acceleration), the truck is reving faster than normal, the truck is still accelerating but its reving high. when its hits 4th its fine. my dad thinks its the cluth plate i think its the transmission, which is it?

When im in 1rst, 2nd, or 3rd gears (only on initial acceleration), the truck is reving faster than normal, the truck is still accelerating but its reving high. when its hits 4th its fine. my dad thinks its the cluth plate i think its the transmission, which is it?

i'm guessing but don't think manual tranny has anything to slip under load like that. my guess is clutch plate worn down to rivets or pressure plate spring tension weak. slipping little under accelerating load but not when cruising in 4th.