Yes, my problem is fixed! Here is what I found. First, the reason the motor only had half the travel it should is that there was a burr on the shaft. Since I had already purchased a new motor from Ford, I installed it ($160). I replaced the connectors at the ends of the vacuum lines at the motor, as one was a loose fit. I then started the engine and tested for proper motor operation, which was negative! I got the vacuum guage out again and tested the lines at the motor--they read less vacuum than before, with even the pink 2wd line reading low vacuum. I then started tracing vacuum lines. I found my problem at a location inside the right wheelwell, below the battery. There is a connector there - mine was very difficult to reach w/o removing the inner wheelwell, battery, etc, but I was able to pull it into view at the lower edge of the wheelwell. What a mess! The connector was mostly separated, and caked with road grime. I pulled it apart and gave it a good bath with brake cleaner and a toothbrush. I re-assembled it and lashed it together with a plastic tie. Re-checking the vacuum, I now have a very solid 20" on both lines! The motor tested good, and the 4wd is now working fine. I intend to go back when I have more time and improve this vacuum connector; maybe change to a different one, or install heat-shrink tubing over it. Incidentally, the operation of the motor is for it to pull the plunger IN for 4wd, and OUT for 2wd.