possible sources of problems could include

1) horizontal centering set screw on the RCA transcoder can cause problems if set to the extreme in either direction

2) you may need to adjust "retrace timings" in the DTC100 menu. This used to be accessed by pressing menu and the down button on the front panel simultaneously, but is now available from the main menu in the "assistance" directory I believe on all upgraded receivers. There are 3 options, one designated for use with the transcoder.

3) the DTC-100 only puts out 540p or 1080i. Many monitors do not like 540p, perhaps the Panasonic included. This was a pretty bad decision by RCA. Sony SAT-HD100 seems to be the best choice for flexibility... I've had alot of software problems with the Panasonic. I think that there is an availability issue, though, with the Sony. Have they discontinued it?