Well, there are several things you can do (in order of cost):

1) Make sure you are using quality RG6 cabling.

2) Improve antenna height - mount it at the top of your roof rather than the side, on a chimney, etc.

3) Upgrade your preamplifier. Radio Shack stuff really isn't that good. Look to the Channel Master 777x series.

4) Unless you're using the VHF portion of your antenna, look to an ultra long range UHF antenna (which will of course be a lot smaller than your current antenna and thus may be easier to move higher). Channel Master and Winegard make some good ones.

5) Upgrade to a new HDTV receiver - newer generation products offer greater sensitivity and better multipath rejection.

6) Do you have a rotor? Fine tuning an antenna's direction can be important to long distance reception, especially when what you want is in different directions. There are IR remote controlled models that I would suggest for convenience.