Other than the conector of the antenna got broken while changing from converter to TV or maybe you did not screw it in properly at the TV I see no reason why the new panasonic (one wold assume it uses latest generations ATSC tuners therefore better at rejecting multipath intyerference) would not perform either equally or even better. I am interested in what Panasonic might say when you tell them that the old converter box works better.

Some TV's like the Sony's indicate also the SNR levels , they should be above 15 db for a carrier lock , I wonder if the Panasonic also has that feature in the signal level screen.