i would go with a 4:10 ratio, that is what my diesel 250 has and it tows great and it dont suck the fuel real bad, second do you have 4 wheel or 2 wheel drive? if you have a 4x4 then you will have to change the front as well.
there are many gear companies out there i would start checking them out. to me i go with the one that saves me money
i got a 5.13 for my dana 44 for 100 bux off of nc4x4.com. U can go on ebay and get some deals on them also. i have to find a set for my 9" now. I may downgrade to a 4.88 instead of a 5.13. im also running 38.5" swampers.