I would check the adjustment in the shifter first. Pull the t-handle all the back where 4 hi should be. Get underneath it and pull the pin out that is in the middle of the flat plate that connects the two shift rails. Pull the shift rails all the way out the transfer case if they are not all ready. Get back inside and pull the shifter all the way back. Get back underneath and see if the pin will go back in. If not you made need to adjust the index plate for the shifter. There are two bolts that hold it to the xfer case. The plate is slotted under the small bolt and washer and pivots on the other. Put the clevis pin back in less the cotter pin and shift it in 4lo. Repeat as above in 4 lo except both shift rails should be all the way in. You want to center the index plate so you have the same over travel at both ends of the shift pattern. If that doesn't fix it maybe something is loose inside the case, the shifter is hitting on something, the hole in the flat plate or the one of the clevis pins is worn on the shift rails or the center pin you removed.