not sure what the "slope" is your pulling your car up,,,,but,,,
eg,,if you use the 50* as below,, and your on pavement,,i think you would be ok...or close.....

Total weight = 3400

Winch pull = 50*3400/60 = 2833

Ground factor = (pavement) 3400 * 4% = 136

Winch load = 2833 + 136 = 2969

hope this helps....

Doug