1998 Isuzu Amigo Slipping?

I have a 1998 Isuzu Amigo. When accelerating in the 3rd, 4th and 5th gear....it seems to slip when u get on the gas! The tach shows the engine racing but the Amigo seems to be taking off a little slow. 1st, 2nd are fine.
The clutch petal height looks good....right in the middle.
COuld this be something other than the clutch??