If the radio connection is like the one in my 2017 Greyhawk it will use the old style RCA connections which is very low res compared to today standards. It has only 480 lines of resolution.
If you want a dvd to play at 1080i or 1080p, which is high def, you need to feed the TV a signal through a HDMI cable. Not possible with an in-dash setup (maybe there is a model out there). I don't use the in-dash for any dvd but rather bought a small Sony blue ray player and connect it directly to the TV via HDMI. The player is small enough to sit below the TV.
No more lousy picture.
Retired electronic technician (45 years in the field)
2017 Greyhawk 29W
solar & many other mods
wife (maybe I should have given her top billing)