3:73 to 4:30 on Excursion V-10

What ever rear you decide to go with, I would suggest it is available in a limited slip, even with your 4WD. Some times you will need the 4WD while towing, but others a simple LS rear will do the trick. Also, realizing you asked about rear ends, another way to make your X tow much better is to swap the less than adequate springs of the X to a set of F250 springs with the "V/B mod" and F350 4" blocks in the rear as discussed at length on all the X forums. Not that expensive, can be done in a day at home by yourself(although I recommend a friend's help) and will make the truck ride and tow remarkably better. I am a true believer now! Now back to the rear ends. If my rear diff ever goes bad, I'll replace it with a Detroit TruTrac. Very heavy duty, no-clutch, low slip differential. I have one in my Chevy dually and it is fantastic. Lots of guys over on the Ford-trucks.com website have changed their rear ratios and have been really satisfied. Good luck in your choice and happy towing/camping with your X.