re: Paid off student loan, credit score dropped 28 points

It is backwards, but essentially paying off installment accounts doesn't improve your score because that account is then closed. The credit rating companies rate you based on your ability to pay back debt. When an installment account is closed, they can no longer measure your risk based off of that account.

It differs with revolving accounts(credit cards) because paying off the balance does not close the account.

Credit Karma sucks and is usually off by 20-30 points. In addition it only gives you your transunion score. However, it gives you an opportunity to see if there are any negatives affecting your history.