New guy needs help

I have read almost every post on this and other forums. I’m sure one of you experianced folk can try to answer one question that seems to stump me.
About what size DC motor is needed to drive a small pick-up ( Dodge D50) through a 4 speed transmision? I have read such terms as 3hp, 6 inch through 12 inch and I am wondering if a 6inch dia, by 12 inches long, rated 36 volts and 3 hp would be enough with the 4 speed? thank you all for your help.
OMG no spell check.

This is a relative question. You need to take into consideration, weight, range, load, and what type of cells you will be using.