Not sure if this is true of all bed slides or not. Seems every unit is a little different. But, on my 2008 Keystone TT I had a similar issue. The bed frame was built really flimsy with 1X2's and 3/8 OSB board. I got rid of the OSB board and beefed up the entire framework and tied the "headboard" end into the slide out wall a lot better. I used 3/4" plywood to sheath the newly beefed up bed frame. I changed the geometry of the strut mounting points so it could handle the extra weight of the new plywood and also the full size residential queen mattress. I have to have the mattress raised when the slide is in so it don't hit the cabinets on the opposing side. Works fantastic.
I also noticed on mine if I sat on the end of the bed to put shoes on ETC the bed/slide would move as the bed is basically cantilevered on the slide. I cut a board tapered to fit snug between the foot of the bed frame and carpeted floor. No more issues. It did add a lot of weight, especially the mattress!, but it sure is more like home.