Same here. When I first got my Diesel and pulled my trailer I heard a loud noise. Thought it was the transmission. But it is the fan that is controlled by the computer.
Sometimes I think mine comes on to often. 65* pulling at 60mph on flat road and the fan comes on. They told me twice that it was OK... So I have to get use to it. We are going to be traveling up some mountains this year and will see how it goes.
As to heat on your legs, I agree with Truknutt, check and see if your heater vents are open.
BC