I have an '07 Dodge 3/4 ton, cummins, 6spd manual transmission, 3.73 alxe. I will be towing a 6,000 lb trailer through Denver today. I am wondering what the ideal speed/RPM and transmission gear would be. Does it matter if I'm in overdrive (6th gear) versus staying in 5th? I pulled this trailer through some hills in NM, AZ & So. CA with it in overdrive over the course of about a 1-10 mile climb and it did fine; the coolant temp stayed below 200 degrees and the engine didn't seem strained in 6th gear doing 60-70 mph. I don't have a trans temp gauge (only stock gauges) so I just want to be safe. Would I be smarter staying out of overdrive and keeping the RPM's under 2,000 while climbing even though the trailer is only 6k? Thanks!