For corn sensitivities, what are the top foods that should be avoided? the lists online are... exhaustive.

Avoid the corniest : It all has to be based on how easy it is to trigger your allergic symptoms. Just having a positive skin or blood test may not mean you have a clinical allergy. If you do, though, start by avoiding the most obvious: corn on cob, popcorn, cornbread, corn flakes, corn chips, corn syrup foods like soft drinks and other sweets, corn starch. Read labels and do your best. If still symptomatic, see doctor.

Diagnosis or treat?: For diagnosis i suggest being exhaustive - i know it's not easy - for about 2 weeks. If you don't see dramatic improvement then you know you are not allergic to corn and you can move on...And put corn back in your diet. If you do feel a lot better you can experiment with adding corn & high fructose syrup back into your diet. That will make things a lot easier.