Just curious ?? Do you know for a fact that the wall and ceiling are square? If it is an older house you could have some building settle or if the walls have been squared to each other and not plum his could be an issue. Do you know if the projector is square to the wall?? I know if an LCD projector block is not aligned properly after servicing it can produce an off kilter keystone effect. You may want to run a laser level against the ceiling/ wall line and see if it's square first. If you don't have a laser level try a level as long as you can find. FYI ,,, I know very little about DLP projectors so take my advice for what it's worth.
Best of luck