Ram power

[slbenz600]

2015 Ram 2500 Larime 4X4 6.4L Hemi, I have remove the coupler and installed dual exhaust from cats out the back that increased MPG but real poor power empty. I can tow 12,000 lbs up and down mountains drops from 16 mpg to 1 to 3 mpg that I beleive it sucks.
I am a certified ASE technician and have taken to 2 different dealers and told me is how it should be. I have owned different Hemi's over the years I owed a 273 Hemi in the 70's that would run crcles around this 6.4L, the 273 was carburator and 6.4L injected, doesn't make sense. The 6.4L couldn't spin the tire even sitting in water, I have a 6.0L car that could chew this up and spit out the exhaust pipe, what is wrong with my Ram ? I have 150,000 miles I keep filters changed and oil change every 6,000 miles.
Tell you how bad this is I went to pass a Honda Accord approximaely 90's model we were going up a 18% hill it was like I turned it off glad I didn't know the other guy he would laugh at me.

 

[rzr6-4]

1) Hemi's are known for making power, however they are also very well known for making that power at higher RPMs. Not so hot on the low end.

2) Messing with the exhaust, and therefore back pressure, may change how things run. Someone more knowledgeable may be able to tell you whether or not it is expected to cause issues, but I know in terms of gaining performance exhaust work requires a tune to actually see much benefit.