can a ford ranger tow trailer on steep mtns rds?

The trailer brakes are supposed to be sufficient to control the trailer. Used properly, in my experience they are with few exceptions.
If the trailer is within the specs weight tongue weight and frontal area that Ford recommends go for it.
You ain't gonna set any speed records in the hauling Olympics,but if you were the kind of guy that was impressed by that,you would own a power stroke or cummins.

Will you be happy? Only you can decide.