I know how you feel Bob. Seems like us home cooks can barely keep up with the corporations of the world that liberally apply glutamates, inosinates, and guanylates to their otherwise lame food. I try to keep up by figuring out new ways to incorporate foods that are naturally rich in these three important food compounds (dried fish, dried mushrooms, seaweed, tomatoes, etc). It may sound weird, but look at a list of ingredients in a bottle of worchestershire sauce and it will start to make sense.
One simple suggestion is to consider the amount of salt you are using. If you made your own rub, it could be light in salt. I take my salt seriously, here's my list of priorities when smoking:
1) is the tenderness right?
2)is the salt right?
3)is the smoke right?
4) is the spice right?
IMO, salt is number 2 but luckily its, by far, the easiest to control.
Another suggestion, and something that I plan to work on this smoke season, is to incorporate into your protocol, a late-stage flavor layer that's a combo of wet and dry. This will be my opportunity to work in things like worchestershire sauce and vinegars (and spice flavors that fade) that will be absent from my initial rub. This concept came from an exchange between me and and Shawn W, and something he dubbed "bark boost." Shawn has already experimented with it some, you can read about it here:
bark boost recipe
recipe application
to mop or not (original thread)
also check this out for some more crazy ideas:
DIY worchestershire
ok, hopefully I'm not over thinking your problem. But this is the kind of stuff that's been in my head this winter.