Got 4L but no 4H?

Boss has a 90 Wrangler with the inline 6 and that and manny transmission. This morning in the snow went to go drive the Jeep and is slipping and has it in 4L.

When he got to work me and another co-worker watched him spin rear tires in 4H but fronts doing nothing. 4L seems to look fine.

Checked the vaccum lines and they look ok and dont seem to be any problem there. Could this be something in the Transfer case? How much would a new one cost or a repair kit of some sort?

Any input is appreciated!=)

Transfer case would be my guess.

is the front drive shaft turning when in 4hi?
if the drive shaft is turning, then my guess would be that it's a problem with the vacume switch on the T-case, or the part of the shift mechanisum that activates the switch.
if the shaft is not turning in 4hi, then I'd guess it's something inside the case.
also, might not hurt to check the shifter linkage, it could be out of adjustment, and not actuailly puting the case into 4hi.