Bill I'm not so sure about an HR54 upgrade. What I think I know.
DTV will not install the HR54 unless you have a 4K TV. The HR54 HDMI 1.4 is not capable of displaying 4K. You have to have the HR54 and C61K mini which has HDMI 2.2. Connect the 4K TV to the C61K mini and another TV to the HR54.
So how many RVs have a 4K TV? Few I suspect. But there are rumors of a HR54 replacement that will connect to a 4K TV and it might also have AT&T internet capability for 4K.
Otherwise apparently the HR54 is much the same as the HR44. In other words no increased capability except for 4K TV which requires the C61K mini.
Apparently the HR54 does not have the external brick so I wonder if it runs hotter. One of the benefits of an external brick is cooler electronics.