I’m having what’s probably the exact same problem. I animated some scrolling text in After Effects then exported in uncompressed video (I’m a perfectionist!). If I then use my compression program the text looks PERFECT. 720×480 @ .9 aspect pixels. I import the uncompressed footage into Premiere in my music video, then I export a few seconds of just the scrolling text uncompressed, then compress it with my program. The text now looks really bad, kind of pixelated and thin, same at 720×48 @ .9 aspect pixels. As the text scrolls it seems to get thicker and thinner based on how many pixels it decides to use at any given position. Final codec used is H.264 .avi file @ 100% quality.
At first I wasn’t sure if it was the export from Premiere or the encode that was messing it up, but after encoding the raw footage I made in After Effects and seeing it perfect, I’m 100% sure it’s the fault of Premiere or some setting within it. I’ve been messing with settings trying to get it to work correctly but no luck so far.