My 2006 1500 Silverado Z-71 has the trailer tow button on gear shift. It has the 5.3L V-8 and I had the factory gears (front & rear) changed to 4:10 ratio. My question is while pulling heavy trailer 7500 lbs, it is constantly changing gears trying to maintain 60 MPH. Every now and then it will shift to highest gear and tach 2,000 rpms at 60 mph but on flat land or least bit of elevation change it down shifts and jumps up to 3,000 rpms. I tried just running the selector in 3rd without engaging trailer tow button and it seems to maintain the 60 mph at about 2800 rpms and of course doesn't constantly shift up or down. Will running in 3rd damage my tranny anymore than the constant shifting?? I had a 1999 Ford with no trailer tow button and I always ran it in 3rd gear. By the way, Chevy is only getting 8-8.5 mpg using trailer tow mode so mileage really isn't an issue. Thanks in advance.