LTD-165H will not read faster than 2x!

when i read psx games the dvdrom slows down to 2x after a while and remains at this speed till finished. it happens with every game at different points and they are not scratched. it will read very fast and then suddenly read real slow but the funny thing is that the rpm stays very high although only reading at 2x.

This only happens with playstation games, other cds like music vcd’s etc read at 48x and faster! Help!!!