I agree with Johnny, you should get that check out in a store. The terms in the "Optimization Policy" are specific in referring to 3G and 4G devices. You may get fed some bull that you are just on a congested tower or something, but it would be worth a shot. I would also recommend printing off the section of the policy that states that 4G devices will not be throttled and taking it with you because I have a feeling the CSR in the store won't know that they are throttling customers, but once you bring it up, they will say, "Oh, well it must be happening to all 3G data users" or something like that. It seems like a lot of times they would rather throw out an easy explanation than actually walking over to their computer and looking into the problem.
They call it unlimited because, while slow, you are still able to consume an unlimited amount of data in a given time frame. There was never a promise of unlimited speed (but that'd be pretty sweet).