How to determine transmission size and gear ratio on Ford TV

I pulled a 34' Carrie Lite fifth wheel from Florida to Alaska back in 1996 with our new F-250 7.3L PSD. No problems. In fact, we had over 200,000 on that single wheel F-250 when we traded it for our present truck. We have owned two F-350 PSD and both of them were and are used exclusively for towing our fifth wheel. Our present 2000 Cameo has over 90,000 miles on it rolling along behind our F-250's.