No, that's not the Equal Protection Clause. That clause, part of the 14th amendment, ostensibly applies the "all men are created equal" idea to actions by the States, not just actions the Federal Government.

I believe you are thinking of the Full Faith and Credit clause of Article IV. But even this is a little different than you think: Full Faith and Credit means that states must (in most cases) respect the individual court judgments and other acts (e.g. marriage) that occur in other states. For example, if I am found liable for a certain amount of money in Wisconsin, and all of my cash is in a bank account in Minnesota, Minnesota must cooperate with Wisconsin to make my money available to the Wisconsin court.

It does not mean that one federal circuit must apply the law that another federal circuit has applied in a different case. In fact, there are tons of examples of different applications of law in different circuits. Now, of course, if the SCOTUS finds these differences particularly egregious to the Constitution, it may step in and overrule a particular circuit's decision, based on whatever part of the Constitution the decision offends.