I have a 2007 Ram Quadcab 2500 6.7. We purchased it used about a year ago, it has 30,000 miles on it. It's a 6 speed automatic, 2 wheel drive, and 3.73 rear gear. We use it as a daily driver and pull our 10500 lb. 5th wheel to Florida for the winter. Last week we were on a 400 mile trip pulling the 5th wheel, at about 300 miles it began to loose power and then set a check engine light, but I eventually got home with it. Took it to dealer the next day, he found trouble codes P1451 & P242f. He ordered parts, yesterday he relpace Diesel Particulate Filter and cleaned EGR system, and cleared the codes. It seems to be running okay. On the Interstate it tows the 5th wheel at 65 mph in 6th speed o/d on cruise control at 1250 rpms. My question is: should the highway RPM's be higher to aide in keeping the exhaust clean? If so, what would be adequate RPM with out wreaking havoc on fuel mileage? Also, will the 6 speed automatic hold up to being run long distance in a lower gear? Thanks for your help.