I'm having a tough time following what you are saying.
When you push the clutch pedal down, can you get it to go into gear?
If so, you get it in first & start letting the pedal up does it feel like it's grabbing?
If that's all working, are you saying it moves the vehicle freely, but at a slower speed?
If that's the case, it may be that the transfer case is in low range, or not fully engaged by the T-case shifter. Sometimes I have to move the vehicle forward a little to get the shift lever to go all the way forward.