Dr. Patel in Austin told me my orange tabby was a little chunky at his checkup, so I switched from free feeding to two measured meals a day. It took about 3 months, but now he actually walks away from the bowl instead of inhaling everything, has anyone else had a cat that acted weird about portion control?
Cats that were free fed their whole lives sometimes develop this thing where they don't trust the food will still be there later. It's not really about hunger, it's more of a worry thing. When food was always sitting out, they never had to think about it. Now with set meals, some cats scarf it down fast because their brain says this might be the last chance. That could be why yours is acting odd even after months. Giving him a little space while he eats and not watching the bowl might help, since some cats get stressed when they feel watched around food.