I switched from a 2004 5.9 Cummins Manual to a 2015 6.4 Hemi Auto, same exact truck configuration down to the gearing. The camper I haul is 2,400# wet and loaded. The biggest thing I miss is the exhaust brake, but have never been worried about the brakes without it. Yes it shifts more and yes the RPMs are higher pulling mountain grades, but I still run the same speeds as I did in the past. Fuel cost wise, because diesel has average 18% premium, it's only costing about $100/year more to drive the gasser than what it would have cost to drive the 04 diesel.
For traveling in Europe, try getting hold of SABConsulting. I haven't seen a post from him lately, but maybe he would see notice of a pm. You can check out his trip reports in the sticky.