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2008 chevy trailblazer_lt
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Discussion Starter · #1 ·
At a point of 50 MPH either accelerating or decelerating, particularly going up a hill when the engine is under load, a hum develops. RPM is around 1500. It appears as though the engine is lugging at that RPM. Give it a little gas and move above or below that point and the hum disappears. I was hauling my small (3600 lbs) travel trailer in "Drive", and it is even more evident.

I took the GM chief mech for a ride. He says the torque converter is not cutting in, and it is quite normal, recommending that I haul the trailer in 3rd in spite of what the Manual says. I always do when on a grade or if the engine is laboring, but I was hauling on a dead flat road when this occurs.

He says there is an upgrade that GM will supply (2008 still under warranty), but you can lose an estimate of one MPG because the tranny will downshift earlier. I am going on my first long trip with the trailer and will haul in 3rd, but the vehicle does it even when I am not hauling. Has anyone else experienced this? I have also learned to downshift now when I drop to 50 MPH, leave it in 3rd until I am back up over 50, then shift back into drive. This is an I6 engine with a four speed auto.

Ian Parsons
Courtenay BC Can.
 
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