WNET-DT posted some information about their new signal
here. The discussion about performing a "double rescan" is especially intriguing. The procedure is basically what I had to do when three of the Denver stations moved from temporary UHF channels to permanent assignments on VHF-high channels 7, 9 and 13.
If carefully following this procedure doesn't help, write back. We'll need more information to help you out, specifically:
-- Make and model of your new antenna
-- Whether it's indoors or outdoors
-- How many TVs are connected to it
-- Whether it's amplified or not, and
-- Your ZIP code for signal-strength info.