Ok, I drive an 03 cts with the clock on the cluster. I know they switched it to the cluster with the temp gauge which is why i am putting that out there. However, i was driving down the interstate today and noticed i was only turning about 1600 rpms at 70 mph. Normally im up around 2350 or 2400. When i got off the interstate and came to stoplight the tac went all the way to 0 and stayed there. the car idled fine and ran fine. i took off kind of hard and everything shifted and felt fine. However, the tac still was incorrect. when i got to work and parked, the tac went to 0 again so i turned the car off then turned it back on to see what it would do. the tac came up to idle speed and seemed fine after the restart. does anybody know what could cause this?