No low end power

Brother in law rolled his 2006 Arctic Cat 400 4x4 with automatic last year. Once we got back onto it's wheels it had no low end power. Anything uphill I had to go up and winch him up. Downhill ran o.k, flatland was o.k. Brought it home replaced all the broken plastic, and adjusted the gear lever so drive was actually in drive position. Took off carb everything looks ok. Changed plug but nothing seems to help low end. Any help greatly appreciated

id jet the thing. i have a 500 and jetting and a filter helped alot. look on www.arcticchat.com and u might find somemore info.

Thanks Catzuki will check into it