Mega sh 2500 hemi how much can I tow comfortably

I wouldn't spend a dime on new gearing. You are WAY over thinking this. Your truck will handle either trailer just fine as it is. I have 21,000 towing miles on my 5.4L/3.73 truck hauling 9,000 lbs without a hiccup. Have crossed over a dozen 9,000 - 11,000 ft plus passes in the west. Have been in 2nd gear many times at 45 MPH up steep grades, but who cares, I'm not racing anyone. The only time in first gear was because I got stuck behind a truck going 15 MPH this past summer with no passing zones.