One recommendation is to start with the meat as cold as possible (but not frozen). A 7 lb flat, if at 35-37 degrees to start, should not hit 140 in an hour. Btw, this is one reason I like packer cut briskets (flat and point); lots more "mass." The flats are just too thin for my taste. Lots of folks like them, so this is just my 2-cents. If you start with a cold smoker, and cold meat, you will maximize the smoke time. Even still, 5 oz of hickory should have given lots of smoke flavor. Maybe you are used to really heavy smoke flavor in your past experiences? Just wondering.
As for rub, I really like Jim Baldridge's Secret Seasoning on brisket, or any beef. Good blend of garlic, onion, pepper, and other spices. If you want a "minimal" rub for brisket, you can go traditional "Texas" with kosher salt and black pepper (not too much) and call it good. Check out the beef section for other variations, and see if something suits your palate.