I dont think after up to temp, mine will even get below 350. I tend to let mine get down to below 400, most of the time that only takes 15 or so seconds, if i was running it hard, ill let it sit a couple minutes before shutting er down.
In the summer time though around here most truck will NOT cool down any lower than 450 even with anything less than 5 minutes of idleing.
As someone else mentioned downshifting does help. A lot of times (if paying attention) I click on the tow haul a a few hundred yards before turning into a parking lot and let the engine slow me down, that seems to cool the temps fairly quick.