What brand do you have? I am on my second Lund. They are pieces of junk. The first time the bug shield turned cloudy it was my fault. I used Invisible Glass Cleaner and the directions say not to use on plastic. My rag would turn yellow when I wiped the shield. I bought a new one and the truck accessory place said to use nothing but wax, particulary anything with carnuba. I used Mother's wax in which he said would be fine, and now I have the same problem as before, yellowing on the rag. He told me that when I used the glass cleaner on the first one, the chemical took out the moisture in the shield that is why it yellowed.
Not sure of the brand? I installed it when I purchased my AV in 03. I've tried bug & tar remover, wax, nothing seems to work. May have to try what Z66 BUTCH and ygmn sugested. I use Mother's wax on the truck. I need to either get it cleaned or purchase a new one, it looks like sh_t.