Since you mention transfer case I will have to assume that you have some 4WD conversion, which is not stock. But you would need to know what transfer case you are running to see if any of the normal post transfer case overdrives (like a gear venders) will work.
I am not aware of any that go between the transmission and transfer case. At one time there was a .75 OD option for the 3-speed Stak transfer case but it did not like sustained highway driving. You get a 3:1 low range but they put a 1:4 gear after that. They were fine ina Jeep at Moab that wanted to make the 6 miles of highway to the trail head, but they self destructed if you tried to drive the 400 miles to Moab.
You can get a transfer case with a lower low range and put more highway friendly tires on.
They do make reduction boxes (typically 2.72:1) that go between the transmission and transfer case. That along with more highway friendly gears.
You could regear the transmission itself. The older AOD gearset can be swapped in and the overdrive goes from .70 to .667 (2/3s instead of 70%). But first gear isn't as low.
