I am not sure if you have the same set-up as the 93-98 rangers do but here goes a very easy fix if it is. I had a '94 manual and here is what I ran into which as it turns out is a common problem with the manual trans of the time. There are rubber plugs in that tranny and over time the crack and shrink. The trans fluid was getting syphoned out while I drove ever so slightly and as a result I was low. I had the same problem you seem to be having and the fix was new plugs (they have billet ones which is best (relatively cheap), or cheaper rubber replacements (OEM style)) and that plus new fluid = a fix. Check to see if the botom for your ranger is coated in tranny fluid. Try the
http://therangerstation.com/ for more info. This is a great resource for the rangers. I would reccomment the billet plugs, noit sure where to get them. GOOGLE them!! Let me know if you need more help. Loved my ranger!!