My sister's family has a 3.5 Expedition EL and the payload sticker is in the 1400 lb range. I'm pretty sure the tow rating is the same 9200 lbs you're seeing. They have a smaller trailer than you, I think about 27' and maybe 7000 lbs loaded, but even so I would be very surprised if they're within all the specs (also three kids and all the stuff you'd expect). Seems to work fine, though.
That said I wouldn't make this change - I like pickups better than SUVs and think they're a better value. We also have three kids and seem to do okay in a crew cab. The dog usually rides in a kennel in the bed, though.
