tonyp063 is correct, 21 and 23 are causing a serious problem for 22, but it is called adjacent channel interference. Co-channel interference would be from another transmitter on channel 22, like a much weaker KCPQ Fox with a NM of -23.3 dB.
TV tuners are not required to tolerate adjacent channel interference greater than 33 dB.
The only possible solution would be a separate antenna, preamp, and a custom single channel bandpass filter for real channel 22 from Tin Lee Electronics. Even they might not be able to design a filter that would work. You could call them and email your tvfool report. The filter would be more than $100.
http://www.tinlee.com/index.php
http://www.tinlee.com/bandpass_filters.php?active=3#CF7