Yes, Keep those Cats. There will be a good market very soon. California is starting Diesel Truck smog inspections and all of the lost and gutted Cats will have to be replaced.
We are driving vehicles that the government and the tree huggers want off the road to make room for their hybrids and compact cars. They'll always use the amount of population that these large pickups produce as their key point in attacking them. Why would we want to go and give them more ammunition? Plus in areas that do emissions testing the truck will fail before even getting to the dyno as soon as the inspector sees the cats have been deleted. Here in Colorado the first step in an emission test is a visual inspection to look for the required equipment.
My 05 had 4" MBRP Cool Duals with no muffler or Cat. At first I got better mileage, but then, after you hear how AWESOME it sounds, mileage went in the toilet.