DavinD- this is a very sad situation, I have kept up with your threads and hoped with a cautious optimism. You have some serious serious considerations to make here.
The 6.0 CAN be a reliable motor but the amount of problems with this particular motor have made a lot of Cummins, Duramax, and Gasser converts.
IMHO... you can't beat the V10 or 6.2 Superduty, 6.0 Gas GM, or the 5.7 Ram Hemi for the "get me home" factor. Same can be said for the Cummins and most of the Duramax lines (first and second gen duramax had some issues... nothing like the 6.doh)
Me personally, I would end up dumping the truck for whatever I could get and I would find me a nice V10 Crew Cab with 4:30 rear axle ratio. 8mpg towing doesn't sound too bad compared to the price for repair you have been quoted. (Despite the perception the V10 is not slow, it is a bit thirsty... but gas is cheap.)
I had one, a long bed crew cab dually V10, and it was a wonderful towing platform. If it would have been a short bed F250 I would have probably still had it. Dually long bed just isn't for me.
Hmm, maybe its time to start hunting that V10 SRW shortbed I have been thinking about.
Thanks and good luck no matter what you decide.
Thanks!
Jeremiah