ISX450.......unrealistic expectations?

[Golfnut]

About three weeks ago I purchased a 2014 Kenworth T680 with an ISX450/1650, 10 speed manual transmission and 3.55 rear end. It has 326,000 miles. I was coming from a Freightshaker with a C12 at 410/1250 with a 10 speed and 3.42 rear end. I'm a farmer and regularly haul 80-85000lb loads and was expecting to be able to comfortably run up and down the highway at 70 mph. After I got it home I had the local dealership (Freighliner/Cummins shop) remove the 63mph speed limiter, progressive shift, and gear down. When I get on the highway, which is mostly flat, I have a hard time getting past 63-65 mph when loaded. If feels like in 10th gear it just falls flat on its face. It has new air and fuel filters (restriction gauge stays very low for both)

Out of frustration I took the truck to a private, well respected shop hoping they'd find something the other shop missed. I just heard back from them and they indicate everything is ok and that I really and short on power and especially torque for what I'm wanting. They say they can up the torque to 1750 but not HP unless I delete emissions, which at this point I'm not interested in doing.

So, do I have unrealistic expectations or do I need to dig deeper? I can post pictures of the engine data plate if it will be helpful.