more 4x problems

i know the topic has been beat to death, but if anyone could offer any suggestions, that would be great! 1999 chev blazer- according to the snap-on modis, the trans is shifting into 4th gear by 15 mph and then trying to lock up the torqconverter solenoid, causing the engine to lug down to about 400 rpms at 18 mph. Now the reason is the tccm is telling the vcm that the transfer case is low range constantly(transfer case low switch-on, or "enabled" on a tech II) Now the dealer mech i talked to said i should look no more, the tccm is the problem. But, for 550 dollars for the part, I'm thinking i want to know if the switch on the transfer case can give the tccm bad info, even though the operation of the transfer case is perfect, it goes into 4-wheel auto, 4-wheel hi, 4-wheel low, and 2-hi just fine and i have made sure of that. Also, i found a vacume line disconnected above the brake booster, the line is hooked into the intake manifold, the fire wall 4 wheel drive vacume switch, the hvac controls, what else is supposed to be there? I've removed the cruise control box looking for any other lines and none are found. :screwy:

Also goes to the vac reservior can in the drivers side fender - a pain to reach but if you feel down in between the wiper motor and ABS right below the ABS mount bolt you see its there.

The TCCM has had moisture in the connectors and possible if you pull the connector in the pass kick panel and dry it may work - also leave battery off for 30 min to reboot in hope that helps. If the dealer used a scan tool and saw a bad TCCM and you say all 4wd ops works then I hope the connector is damp!

Thanks for the help- went straight to the reservoir and found it with no problem. whoever thought of putting one there ot to be shot!!
As far as the tccm goes, The dealer didn't see a bad one, I was looking at it with a modis from the shop I worked at for 7 years, until some drunk goober hit my boss when my boss was on his bike, shop is now closed as we laid him to rest and I, at the moment, am out of work and have no diagnostic resources. Checked the plug as you had mentioned, no such luck. New TCCM did the trick.
Thanks again..