well im running 41's with a 9'' and 20x12 wheels. i had to trim the fender a little. i bet you can fit 38's on a 6'' with the right wheels.
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2006 cummins 3500 laramie murdered out
13.5'' lift, 20x12's on 41'' iroks
TURBO ENGINEERING CORP. 617hp, stock cp3,stock lift pump, and on 41's
custom paint and amp step getting done