i have 05' suburban 1500 4wd,5.3 w/4.10 gears. @ 2200rpm =70 mph ,with 30.7" tires. i put on new firestone destination a t's.285 70 17's. does anyone know my new ratio? i was trying to lower hgwy.rpm @ cruise. are my gauges still accurate (tach, speedo )? should my computer stiill be accurate ( on truck ). thanks len