Have you got.a.body lift......sometimes hole in floor needs a bit of persuasion as too small....TJ may be different but that used to be a YJ prob.....
I used this method when I had a transfer case drop before getting my SYE and driveshaft. Can't remember which way the lever at the transfer case shifts to go to 4L so have a look at it in 2H and 4L from underneath so you know which way it goes. Put the shifter in 4L and trap a 1/8" drill bit or screwdriver shaft that size between the shift lever and the gate. I did this from in the Jeep and used a bit of tape to hold it in place. Undo the trunnion bolt them make sure the transfer case is in 4L by moving the lever at the transfer case. Tighten the trunnion bolt and remove the drill bit/screwdriver. By setting the lever with that 1/8" spacing between the lever and gate it should mean slack in the linkage is taken up and the transfer case fully engages 4WD.
The body lift should have come with a drop bracket that fits on bracket no 8 in the diagram but try the adjustment first
