I bought a 04 3500 ,cc ,lb, lly ,allison tranny ,and edge juice and attitude moniter with 250,000 miles about two months ago. I tow a trailer every day to work that wieghs about 7000 lbs. When in tow-haul going down hill at about 45 to 50 mph it shifts down and rpms go up to 4000. Is that normal...