You're right, it's not 3G:

    Me:  On a plan that says "First N GB at 4G speeds", what
         speed do I get after I hit the cap?

    Rep: Once the allotted high-speed data has been used
         speeds will be throttled down to our 2G speeds.
         This would be comparable to about twice the speed
         of dial-up which translates to about 100 kbps.

Thanks for the correction!