Al, Shift the RD to the cassette's largest cog, then without pedaling shift the lever downward and you should have eight detents, or clicks through it's full travel. If not the shifter may've been switched from friction to SIS when not at either extreme of it's travel. If you are at either limit of travel, IIRC, you should be able to switch to friction from SIS and back again to regain all eight detents. Is the overshifted gear always the same?

Brad

PS Yes, I have the same 7700/6500 combination