Check the sticky at the top of the AGR forum for info on known promo codes. Trust me--all the codes anyone around here knows are posted there.

Direct link here: http://www.flyertalk.com/forum/amtra...discounts.html

Sleepers take up a lot more room on the train than a coach seat and are in a much more limited supply, which partially explains the price difference (as more get booked, the price goes up, so if there are 30 sleepers on a train and 20 are booked, it's going to be high, where there might still be 200 open coach seats). Also, the price is per room, not per bed, so the sleeper charge (though not the base railfare) is the same for either one or two people (i.e. find a person to travel with and your fare gets cut almost in half!).