Have a 07 trailblazer, L6 motor. Does anyone know how to tell if their Overdrive is working or not? Sounds stupid, but the truck shifts through all 4 gears, but doesn't seem to go into overdrive gear. It appears the rpms are all correct at shifting intervals, but on acceleration the engine seems loud , and once on the highway it seems loud also, and I am still at 1800 to 2200 rpms. When I got the truck a few years back, you could hear it dog out for a second, and I knew overdrive was engaging. Now all I hear is loud engine sounds in 4th gear, even on deceleration. Thanks for any help.