Time of decision: 2004 4.4 approaches 100K

[grasmere10]

Here's a business/mechanical/probability problem that just stumps me.
My 2004 4.4i has 96,500 miles. Another 1,000 left on paid-in-full extended warranty.
I love it but bought it in April 2008 (with 39,000 miles) - just before gas prices jumped. Consequently, I am underwater on the loan - by $6-$9K net (depending on whether I take the lazy man's route and sell it to Carmax for 12, or try to get 15 for it privately).
So - do I buy my own nearly 100K X5 for 21,000 or do I buy a low mileage used 4WD of some description that costs a total of 31,000 - (car for22,000 + 9000 net loss on X5)?
If I keep it - I see Warranty Direct will sell me a warranty for my next 25,000 miles (about 18 months of my driving) for $5,500. This tells me that they're betting my actual repair costs will be about 2,750. Of course, they could be $11,000. If I didn't buy myself out, I would reduce the payoff amount of my loan by about 8,000 bucks - perhaps resale value would diminish by 6,000 in the same time period.
During my tenure, the car has consumed a new alternator - no other trouble.
Oh - and one other thing - the dreaded "clunk" on re-acceleration has begun. See other threads.
So - if you were lucky enough to trade places with me, what would you do? (Don't laugh - some guys would: my wife is pretty and my tires are new.)