I would kinda suggest to think real hard about a ford. We have the 6.0 liter in our ambulances and they just seem to have problems. Yes we are a little harder on them than most but that means problems show up sooner also. It isn't the engine itself usually but sensors,EGR valve,injectors,glow plugs,filters,etc. Some sensors will put you down now,no warning,and no way to bypass and limp home. The biggest problem was a couple of trucks in the fleet went through head gaskets and turbos. There are some of the later 6.4 liter engines on the road but I have no experience as they are on the other side of the state. The company just bought 30 new rigs with the V10 gas engine because of the diesel problems and they will be converted to propane or CNG in some areas. My part-time boss a few years ago had 2 new Dodge tow trucks. Both were 6.7 cummins with the new automatic and the engine brake. Nice running and steady,strong torque,like a docile locomotive. One is a 4500 2wd and the other is a 5500 4wd. The only problem that I heard of was complaints about the huge smoke cloud when it did a particulate burn off. Think white steam like smoke that is so intense that you can't see behind you at all. It makes you think that something is seriously wrong. I don't have any experience with the GM duramax engine because I don't know anybody that has one. My GM friends have the newer 5.3 gas engine and are thrilled to death with it. If money was no issue,but it is,I would get a dodge mega cab with the long bed conversion,diesel,6 speed manual tranny,and 4wd. I don't have too many issues with driving a large pickup in the city. I have figured out the turns and parking needs a long time ago.