Gerard, I have a similar problem with my 1275, 5speed and 55 series tires.
I've stuck with the 4.22 to give me the low end torque since the motor is
set up for high end hp. In trying the 3.9 I was never happy with the the
low end torque. If you do mostly freeway driving you'll like it. If not
stick with the 4.22.
As for the noise, I've already lost some hearing so I just put in the
ear plugs and putt on down the road.
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