First, yes you are correct that based on the information given, does not
sound like a power steering issue. You state the noise goes away when it's in neutral so this tells me it is not an issue with a wheel bearing.
Also, you say it doesn't do it while it's in Park and revving it up so it makes me believe it is a transmission issue. When was the last time the fluid was replaced?
Originally Posted by skateillini
I am pretty sure my truck has the towing package, which I believe means it has a transmission cooler. Is there a pump for it?
Yes! The "Trailer Tow Group" includes 160 Amp Alternator, HD Cooling System, and as you guessed Auxiliary Transmission Cooler
. Check the lines going from the cooler to the transmission itself and ensure there's no leaks or anything that looks out of the normal.
If you're feeling lucky, I'd try getting a friend/wife/girlfriend and put the rear end up on jack stands and hit the throttle as if you were driving (in Drive). MAKE SURE IT IS IN 2WD ONLY! Get under the vehicle and isolate the problem where it is coming from and most likely pay attention to near the transmission area, that's what I'm thinking it is.
My first possible solution would be to start by doing a full transmission fluid replacement and checking the pan for any signs of anything wrong such as metal in the pan or inconsistent fluid color. When you do a fluid change use nothing except ATF +4, I've heard of problems like this due to puting the wrong type of fluid in.
Also, since you claim the noise mainly comes around when the engine is up to full operating temperature, it may be the Torque Convertor. Try driving with the O/D OFF
on the gear shifter pressed in to turn off the Overdrive gear and see if that possibly helps.