Why don't you trade that F-150 and that grand cherokee in on some gas 3/4 ton that isn't going to blow up when you tow with it? They can be had at a price where you won't have a payment.
The front seal let go, probably due to improperly installing it when it was rebuilt 12k ago. 3/4 gas = no. An F150 with the new "max tow"package is suppose to be pretty decent gas hauler, but 30-35k for an XLT 4x4 is more than I need to spend.