Repost; Can't get '95 GMC Jimmy in 4WD

Sorry about the repost... someone sent me an e-mail asking for more info on exactly what is wrong with the Jimmy, and when I replied the e-mail bounced back as a bad address.
Our 4.3L V6 Jimmy will not go into 4WD, a problem we discovered after having the auto tranny rebuilt. The mechanic checked the switch and electric & vacuum lines & everything tested ok. He said the transfer case was getting the signal from the switch but that's it. Neither he nor the tranny shop who did the rebuild could find out what's wrong. The mechanic used an Alldata printout to troubleshoot if that helps.
The switch shows 2wd all the time, even when 4wd is pushed. This has been our experience; the mechanic said at one point all the indicator lights were on, which has prompted him to swap in a new switch. Did the same thing.
The mechanic & tranny shop are stumped, they think it might be one of the electronic controls (I am so clueless about 4wd mechanics it's not funny!)
Thanks in advance!

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