How to determine transmission size and gear ratio on Ford TV

Try any ford VIN decoder to see what the spec are on truck. And also look at door sticker of "axle group" Then there should be a axle tag on rear diff. get the numbers off it and look it up.

http://www.google.com/#hl=en&gs_rn=12&gs_ri=psy-ab&cp=7&gs_id=s&xhr=t&q=ford+vin+decoder&es_nrs=true&pf=p&output=search&sclient=psy-ab&oq=ford+vi&gs_l=&pbx=1&bav=on.2,or.r_qf.&bvm=bv.45960087,d.cGE&fp=771fa58581d29b28&biw=1366&bih=622

http://www.google.com/#hl=en&gs_rn=12&gs_ri=psy-ab&pq=ford%20vin%20decoder&cp=13&gs_id=3p&xhr=t&q=ford+axle+tag+codes&es_nrs=true&pf=p&sclient=psy-ab&oq=ford+axle+tag&gs_l=&pbx=1&bav=on.2,or.r_qf.&bvm=bv.45960087,d.cGE&fp=771fa58581d29b28&biw=1366&bih=622

Takes awhile but worth it. I thought I had a 4:10 ratio but using axle tag have 3:73 Also while under there changed diff grease/oil. Never thought I would spend $20.00 a quart for oil but that is what it goes for.
Hope this helps.