I put in the biggest they had at the auto store. 20,000 GVW rating tubular unit.
Like this..
http://www.amazon.com/Flex-lite-4120-Translife-Transmission/dp/B00029J3WKAlso as far as trans temps, once you get near 200f varnishes start forming IMO. I only use synthetic in the trans too...
As far as the engine temps thats way too high IMO.. Maybe you need to check the coolant %??
I would be looking into an oil cooler possibly . ( Synthetic oil too.)
Its your truck though and its just opinion.
I personally run as cool as I can. Heat kills...I can tow all day and not reach over 180f.