Do a flour dip, then into egg and milk bath, then into your final breading. Guy hit the temp, that is about right, make sure you are at least 350. When they float, they are done. Hard to say what you are doing wrong but probably not hot enough.
You want really good fried fish. Take a skillet with and cook them over hot coals on shore, in butter. It's been a long time but it is the best. I grill walleye and every other way you can cook them; I've come to the conclusion they are the perfect fish to fry.