Since there were no direct comparisons here is mine.

I have hand calculated lots of tanks and the computers on both have been surprisingly accurate.
70% highway, 20% country roads, 10% city

My numbers are in the format: best hwy/best avg/easy avg/winter avg all in L/100kms

2016 2500 SLT with the 6.7 Cummins, 3.42 gears, everything else stock, unloaded = 7L/9L/11L/14L
2013 1500 Laramie 5.7 Hemi, 3.55 gears, everything else stock, unloaded, = 11L/17L/21L/30L

I never towed the same loads with both trucks so I can't provide any comparable towing numbers.

For additional comparison, I had a 2009 F150 with the 5.4 and 4.10 gears and at it's worst in the winter it was at 22L/100kms.

I am not saying the Hemi is bad, I just think that Ram put the wrong combo of gears and tires together on that one.

 

We have 2006 mega cab 2500 5.9L diesel. We go to Colorado mountains. We need 4x4, 4 door to pull Rv 7,500 Gw. We are looking at the 2018-19 Dodge gas hemi 2500 or Ford gas F250. We heard Ford is really a gas guzzler. For gas mileage, sounds the hemi is best, but what about towing? Would the Dodge 1500 or Ford 150 make it?

 

According to theory, either of those half-tons would pull your trailer, but, I would still recommend going to a 3/4 ton. Getting it moving is one thing, making sure you can stop it is an entirely different matter, the MUCH larger brakes on the 3/4 ton trucks would provide for a lot of peace of mind.

The Hemi will likely drop into single-digit gas mileage when towing, especially in 'hilly' terrain.

 

Thanks.
The hemi is new to us. The salesman made it sound "fuel economy". We drove the only thing he had, a 2018 gas Tradesman 2500 4x4 CC short box, white. The drive was ok, stop & go, freeway, over RR tracks. It was a real "plain Jane".
After 3 wks shopping, we may be sorry we did not buy. He would not deal much on price.

 

Yeah, the newer trucks have MDS. (multi-displacement system) and will shut down cylinders in low power demand situations. I would think it would be disabled in tow/haul mode though.....

 

It is disabled in tow/haul in any MDS Ram even the 3rd gens