I'm bummed that your proposed mod didn't end up seeming advisable. If I saw temps like that on my E-350's transmission -- even towing up a steep pass in hot weather -- I would not be pleased (luckily I don't though).On long drives with short stops(gas/food), i'm seeing temps from 210-220f (in 95F weather) on my ultra gauge when i restart the van. So this is still on my wish list to do.
This is one of my biggest worries about running a Transit. I mean, it's all good if you don't do things that raise the transmission temperature (which seems to be the case for many, which is great). But once you do..... there doesn't seem to be much in the way of options to make it any better. In this way it seems completely unlike previous vans.