just to report back to help others...
Got it back into 2 hi- played with control module plug (behind right hand lower kick panel) several times pure persistence - for I'd say an hour or so .. still not working ... left truck from disgust .. came back 30 mins later and tried the switch and it was working !!!
it went back into 2 hi and I decided best to leave well enough alone and never tried to switch it again for fear it might get stuck..
Ryan