George, you'll master it. I t just takes a few attempts and some adjustments. Follow Nick's suggestion on temp. Check the brisket at 185 and if it feels soft and tender--your probe enters effortlessly--it's done; if not, wait till the temp goes up a couple degrees and check again. If you wish you can add a little liquid to the foil when you first foil (recommended if the flat is on the thin side) or when you pull it to rest. (Beef stock, say, 3/4 c mixed with a pat of unsalted butter, or half that plus a portion of your sauce are just a couple of the possibilities. If using canned stock I'd recommend a 50-50 mix of beef and low-salt chicken as canned beef stock is notoriously tinny regardless of brand.)
In the first scenario you'll create a braising/steaming situation--not necessarily necessary if the brisket is well marbled but if it isn't, or if it is on the thin side, it can help the juiciness factor. In the latter scenario: Meat has an increased capacity to absorb liquid as it cools, so during the rest some liquids/flavors can be absorbed. Excess liquid can (should, imo) be added to whatever sauce you've made to add 'meatiness' and to tie it better with the brisket.
Give it another shot and let us know how it goes.