The 2wd '86 Ram50 I had was a high-altitude model...but I'm not sure what differentiated it from the low-altitude models, though presumably it was stuff like carb jetting and timing. I don't think the gearing was any different (it had great highway gearing) but then, it was only a 2wd.

I've always heard that the 4wd trucks and Monteros (high-altitude) had the 4.88 gearing, but I've nothing to support it.