Wearing bike shorts? Maybe try the tires inflated on the low side of their range? Not sure whether or not the seat post pre-load is adjustable or not, if so, maybe play around with that. If you are bottoming it out, make it a little stiffer. Remover the seat post and see if there is an adjustment screw on the bottom.
The aluminum frames are more harsh, have you considered a 7200 instead? The front suspension might help some, and it's only about $30 more.
Were you riding that Mongoose recently, and now making a transistion, or have you been off a bike for a while?
"It hurts so good..."