I don’t know for a fact that the mounts are different. I’ve seen a few parts listings that would lead me to believe that there was some change. Below are a couple of examples:
This page shows front hitches and tow plates for 84-98. I guess that they don’t fit ’99 and up?
http://www.quadratec.com/cgi-bin/sgsh0101.exe
Also, this skid plate is listed as ’97-‘01
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7934476640
The stock front bumpers as well as the aftermarket brush guards are also separated in the same year groups. I believe that has more to do with the way that the end caps rap around the bumper/fender than the actual mounting points. I have factory parts listings, but mine only go from ’84 to ’96. I’m not able to compare part numbers, but a pre ’96 is listed as part number 8220 0613 PLATE, Front Skid, Axle and Steering. If some one has a part number for a ’97 and newer skid plate that would be an easy way to tell.