I read through the manual and Kia cautions about towing it for any distance. I did see the recommendation to tow with the transfer case in 2H and 55 mph/50 mile limit. You are of course not under warranty, so what you do with the vehicle is on you, not Kia.
Remco is a pretty reliable company, they list your vehicle: "2001 Kia Sportage Base, 4DR 4WD I-4 2.0L cyl 4 Speed Automatic 03-72LE/RE4E01A
Must be towed using a trailer
Store : Remco
Parked on a flat space, put the transmission and transfer case in neutral. Try pushing the car by hand and see if you can detect transmission motion. You could also try towing it for a short distance and then checking the transmission temperature by putting hand or IR remote sensing thermometer aimed at the case.
If you really trust the previous owner, tow it for a long trip and see.