CHanging rear end, paccar motor

[Rounded_nut]

Heya folks, long time no chat. Anyways, I got a 455hp MX13, EPA2013, 13 speed and 3.08 rears. It's been doing just fine with the usual light loads (10k lbs), however I'm leaving that gig and will be at gross everywhere but a fair amount of NW, so mountains. I'm looking to swap out the rears to 3.7x, used/rebuilt, however I'm wondering about cruising rpm's, specifically how the engine performs cruising loaded at 1400-1600 rpm. Torque peaks at 900, rpm limit is 2200 so I'm thinking it should do just fine at 1500 rpm, just not sure how this pushrod engine likes it. I know just by giving it a better lever that'll help, as well I don't intend to keep it floored going up the hills. With the god awful 3.08 rears a gross load over a speedbump is rough enough!

Adding on, going with used/rebuilt carriers does $2k sound about ball park to swap out?

Running low pro 22.5.