Got my new truck all rigged for the trailer, now have a question please. It is recommended not to exceed 50mph for the first 500 miles when towing to continue breaking in the rear end with a load. I understand that they get pretty hot until wore in a bit. I have good intensions, but am short on patience, so expect to go from 50 (for awhile)) to 55 to 60 to 65 and then my usual 70 mph, probably in the first 100 miles. Anyway, what is the minimum RPM while towing 9,000 Lbs ? Stay in 4th or lug in 5th I guess is the question. Thank you and have a GREAT holiday season !