A couple of things here...first, back when I started smoking pot in highschool, a few hits would keep me high all day. Now, I also come down pretty quick. I think it's tolerance that built up over time...if you take a couple days off, or assign yourself to only smoking late at night after dinner, you may notice that you feel more stoned than you did when doing it all day everyday. Also, a better strain/higher grade weed may help --- yeah, it'll cost more, but you'll need less to get high, so less damage on your lungs and more efficient in the long run.
Second, I, like you, absolutely loved my xanax prescription. Relieved my anxiety, just pure awesomeness. I currently do not have one, and have about 8mg to last until I hopefully get a psych appointment in about a month and hopefully get my script back. Going from taking it whenever you feel the least bit anxious to not at all/only in very isolated episodes is absolutely awful when you are used to having it there for you...I also find that pot helps me stay away from it to some degree. In another thread, I mentioned that just like pot, benzos also increase my appetite, and I also feel as if I need one or the other to exist.
So, OP, I understand where you are coming from quite a bit with the xanax thing...in sum, my advice: better quality weed, and smoke less often (I know how difficult the latter is, but after an all day everyday for way too long affair I've finally got myself down to nightly only unless there's some event causing an exception to this. When you come down from being stoned and are still awake you tend to just feel shitty and wanna smoke again, so only smoking at night I've noticed avoids this).
I also disagree with double ewe that because of xanax, pot isn't cutting it anymore. Even without xanax, pot still works just fine on it's own...I just feel as if the two chemicals worked very similarly for me, but I never really found benzos to enhance the pot high all that much, nor found benzos to be very recreational at all.