I told my wife we would not drive a big DP unless we had the checkbook in our pocket. Driving one from Calif to Colorado convinced me of the advantages for going full time. The exhaust brake is wonderful and keeps the service brakes from being used much. Very quiet compared to any front engine gasser.
As for power, those with the ISL's you can get a huge improvement in power and some mileage improvement adding a very easy to install module. DIGI CR power module from Parleys Diesel. If you have a rear radiator fan that is the fixed pitched model and not the Horton fan you can change that and gain about 30 HP as well and improve mileage. I easily average 8.5 and my mountain climbing is much improved. With the two mods I am running close to 400 hp at the rear wheels and close to 1200 ft/lbs of torque. That is rear wheel power. If you want more info PM me. Don't want to hijack the thread.