First, hook your existing antenna up to your TV or another OTA tuner to see if it receives your problem channels better than the Premiere. If you find that they do, you may live in an area with dynamic multipath signal reflections, which the Premiere cannot handle well. There's no antenna you can get that will compensate for the Premiere's shortcomings in that regard. On the other hand, if you find that your other OTA receivers have the same reception problems, you can continue troubleshooting with antennas etc. A good place to look for guidance is the AVS Forums Local HDTV Reception subforum. Here's
the NY, NY OTA thread. If you rule out the Premiere as the cause of the problem, give that thread a read and maybe ask for some help there.