no 4wheel drive

on my bravada 2000 olds we have no 4 wheel drive. We replaced the transfer case shift control module, and the encoder motor still no luck . when we put encoderer motor on we could not rotate the shaft. had to line it up with the 4 wheel drive to put it on but still do not have 4 wheel drive. have checked all grounds all are good. Whats next?

Have to put it on a trans scanner - those AWDs had some serious transfer case issues and GM switched to special blue syn transfer case fluid (dealer item at $7.50 qt and takes 2). They have clutch packs in the case that can get burned up - bulletin on them that says change fluid with blue, drive 100 miles, change again - if that does not fix rebuild - sorry.

In addition to Muddog's explaination, you might check to make sure the front differential has plenty of lube to handle these stresses.