What gears are you running? I am jumping on the 66mm bandwagon soon myself. Going with a T4 box Borg though and adding an exhaust brake. This is on my tow rig which grosses 26-35k lbs when in use. I usually don't let RPMs drop below 1800 and they are usually in the 2-2200 RPM range.
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95 2500 4x4 G56 180 pumped 4k 362/475
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