Joe, one thing that will cause your wood to burn up too quick is poor-quality (dry) wood. I use 6-7 oz of good quality smoking wood on butts, and have never had anyone complain it wasn't smoky enough.
You mentioned "can't add more wood." You should never have to open an SI and add wood. First, because the element is at a "maintenance" temp, it will be hard to get it smoking again. Second, and most importantly, is that the meat has already absorbed all the smoke it is going to, once it hits around 140 internal. After that, the smoke pretty much piles up on the surface of the meat, much like the walls of the smoker! Maybe you're used to over-smoked meat, but most don't care for the bitterness of creosote-flavored bark.
Bottom line (imo)- get some good wood (like smokinlicious.com) and see if you don't get better smoke.