Have 2010 dodge 2500 diesel, 2011 Grand Cherokee 5.7Hemi and 2011 Winnebago with Ford V10.
One thing I can say is I would not make the exhaust brake a big deal anymore. The tow/haul mode in all 3 of my vehicles above is just awesome. I have towed 7000lb loads with all three vehicles down 6-7% grades and the tow/haul really is that huge of a difference. I cannot use the exhaust brake and tow/haul mode on my truck, it just slows me down way to much.
As far as longevity. Diesels engines may last longer, but everything around them breaks and costs way more than the gas counter part. Diesels cost more up front so you better get more back on trade it.
The only real argument on Diesel vs gas is power. Gas is not even close to the power of a Diesel. If your pulling 9,000lbs frequently I would not even consider gas. If power is not a concern for you then gas may be the way to go as it is cheaper in the long run.