Jason, the short answer is that very likely you’re not doing anything wrong.
I’ve mostly given up anymore trying to troubleshoot and QC the stuff I send to stations. When I’ve spotted things on air that looked like crap I’ve called the stations and get some twenty-year-old on the line who usually says, “Looks good to me here”, which usually just means he sees an image and hears a sound.
I’d say that if you’re checking your stuff on a CRT monitor and it looks good, and the files you’re giving stations are to their specs, I’m not sure what else to tell you. Some others here may have more specific and illuminating advice, but I’ve been creating TV spots for over twenty years and never had problems until about a year or two ago.
So much has changed and there are now so many variables that I don’t know if the target will ever stop moving enough to (consistently) hit the bullseye anymore.
–Kelly