It sounds pretty clear to me that the problem started with the replacement.
That said, try to adjust the output resolution of the Dish Receiver. Many of them come default with a 480i/p resolution, so changing the output resolution in the receiver's menu may provide a better picture.
If that doesn't work, then call Dish back and ask for a replacement/upgrade, assuming that other inputs look just fine.
LN32B650T only a year old, was working fine until couldn't get satellite signal. DISH sent out replacement receiver. Now the picture is awful. Mostly reds, pinks and green. Dish says the problem is with my TV not their receiver. Any suggestions to fix this?