If you really want the low range in your 2wd truck, find one of similar year and same configuration, single/ext cab, long/short box ... but is 4wd and being parted out.  All you will have to do is take out your 2wd trans and tcase and swap in the 4wd trans and tcase.  If that doesn't work, find a divorced t case and put it in there.  Linkage shouldn't be too hard to figure out but make sure you have enough room for good u joint angles on the rear drive shaft. One more thing, for 88-98 GM trucks, some came with a 5 speed manual ( I think the nv4500).  It has a low 1st gear and an overdrive.  If you like autos, some of those same year trucks had 700R4's (4 speed auto - overdrive) that have a decent low first gear.  Make sure your axle gears are matched for your tired size or you will burn that trans up.  There are a lot of choices just depends on the work you want to do and the money you want to spend.