I may take a facepunch with you but here is my opinion...
I have a 7.3l diesel F350 that I use sparingly to haul loads (dirt, equipment, hay, mowers, building materials, scrap, yard waste, etc). As a result the yearly maintenance/diesel/registration is very reasonable, certainly less than I would spend renting a comparable vehicle for what I do. Additionally, the 7.3l has never lost value from where I bought mine in 2008 (bought for 7k, worth about 8-9k today). This is due to the fact that my 4wd 7.3l could still be put to use for a few good years as a plow truck I believe.
So I say keep it, use it for what you want, but at least consider canceling comprehensive insurance for collision only with the mindset that you can further minimize the current cost. In that situation your only loss is keeping the money parked in the truck. And in that instance 6-7k is nothing compared to having a vehicle that can move your home (RV) at a moment's notice.