99 Blazer 4WD not working, replaced everything

I have been fighting with my 4WD since this summer, trying to get ready for
the winter.  I've poured over countless posts and YouTube videos on it, and
I have replaced everything I can think of.  

The problem seems to be standard - after resetting the Transfer Case
Control Module (unplugging for a couple of minutes), you press the 4WD HI
button, and it flashes, the relays click, then it just reverts to 2 HI after about
10 seconds.  Do that about 3 or 4 times, and it just clicks once and goes
back to 2 HI.

I got the blink code from the TCCM initially, which showed a bad transfer
case actuator.  I replaced that, and same problem.  

I replaced the vacuum actuator underneath the battery tray.  It showed
signs of having fluid in it at one time, so I thought that might be it - nothing.  

I replaced the vacuum valve on top of the transmission.  I re-routed all the
vacuum lines coming from the vacuum valve on top of the transmission -
there are no leaks.  

I read that there was a problem with transmission fluid making it into the
vacuum system, but the other vacuum actuated valves for routing cabin air
work just fine, so there is apparently vacuum available to run valves.  

This version does not have the 4WD actuator solenoid valve like this one:
http://www.mypartsgarage.com/dorman-4wd-actuator-valve-600-104.html?
gclid=CjwKEAiAvauyBRDwuYf3qNyXmW4SJACX9-
fXEgJ8C_qsV9WKLJWY8ds_9hWwVFgV6T3Z-YW26bHusRoCYjXw_wcB

There is a vacuum resevoir in the driver side fender, which I found the
vacuum line disconnected from.  I thought AH HA!  Finally something visibly
wrong.  I reattached that, and still the same problem.  

Even though there was no corrosion, and I could hear the relays clicking,
as a last ditch effort, I replaced the TCCM.  Sure enough, same problem.  

To the best of my knowledge, it is a 100% completely new 4WD system.  
Does anyone have any idea what I could be missing?  Thanks for your
time.