The $64.OO Question is..... Does your Cruise control work?
Now I know your thinking "why would Brett ask if my cruise control is working when I have a speedometer problem?"
Let me explain. The P30 chassis being a GM product suffers from some of the GM quirks. The Speedo cable comes from the transmission to a box (under the drivers side seat on my argosy, directly above the left wheel). From this box a cable goes to the Speedo. The box in question is the cruise control. If you lubed the upper end as you described, you have not added any lubricant to the lower speedo cable. The lower cable has a tendency to bind and SNAP. This will not affect the ability of the MH to go down the road, but you will not be able to drive thru Waldo, Fl.
My reccomendation would be to lube the lower cable and see if it helps. If it does snap you should be able to replace it youself as long as you do not mind a little grease.