F150 3.31 rear axle vs 3.55

[Daniel Nawrot]

I need to know real experience if an F150 (3.5 Echo boost) 3.31 rear axle is strong enough to pull 8,000lbs up 6 & 7 % inclines that are several miles long, OR do I need the 3.55 rear axle?
Thanks,
Daniel

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