Without the zboost I have less then one bar of signal, with the stock antenna I did get better signal about 2-3 bars, I got the best antenna with the flat pannel and the little vhf looking antenna too and they helped a lot because you can point them at your closed tower, also the pole I have the upgraded antenna on is PVC not metal zboost told me that metal would interfear with the signal
Also I'm sure you know that best place to test your phone is about 5 feet away from the zboost, and I know this stuffs not cheap but you might want to get the better indoor antenna to, I don't have it but it will give you better distance in your house.
And I don't know how long you have had the booster but I only get about 8 to 12 months out of one befour I need to replace it, for this reason I turn it off when not in use to increase the life of the booster and it's been working over a year now.
My Droid likes to switch down to 1x I just close what is using the net or restart the phone to get my 3g back and put the phone next to the booster when I want to download my podcasts, it's not perfect but it works most of the time and it lets me live out here and with some internet.
Hope this helps.