Channel change intermittant from remote or control panel

Channel will not change from the up/down on remote or control panel, condition is intermittant, tried 3 remotes from Hitachi, Tech changed the IR Receiver pcb in set-no help. Up-graded to v0108 firmware. I am connected directly to the Cox Cable (no set top box). All other function buttons on the remote work every time. When the channel will not change the channel number does not appear on the screen and sometimes requires 2-4 deppressions of the channel up/down to finally get to the channel indication on the screen, and does the same when using the up/down on the set control panel. (I understand the delay that is normal in the tuner change -after the channel indicator display appears- !) Hitachi has dragged their feet on additional tech visits or action for 5 months. I have visited show rooms with this TV and used my remotes, finding them to function without failure. Hitachi is sending me the latest F/W (V0110.) will see, the help desk could not tell me the fixes included. Anyone else seen/fixed this problem ??? Thanks Moonie