It does sound like you got bit by the 480/486 thing. Uncompressed "D1" video (486) makes up for the oddball half-line that NTSC has top and bottom and it's slightly larger than the consumer grade 480 which just pretends it's not there.
By the way, we create graphics at double both directions--1440 x 1080. When we get the graphic perfect, we resize it to 720 x 486 with constrain proportions turned off and the resulting slight softness gets rid of interfield sparklies and flutters automatically without adding any more overlays or filters.
Koz