4WD doesn't disengage properly
 

I have a 98 Chev S-10 Blazer. I have no problem shifting from 2hi to 4hi, 4hi to 4lo or from 4lo back to 4hi. My problem is when I try to shift back into 2hi. You can hear the transfer case 'clicking', and you can here the TCCM relays activating. The switch light on the dash momentarily goes from 4hi back to 2hi, but then it kicks back into 4hi where it stays. I've check the electric shift motor and it seems to be OK. I've even went as far as getting a new transfer case from the wreckers for comparison, and the transfer case appears OK. I've had my budy under the truck when I try to go back to 2hi, and the drive shaft momentarily disengages (goes back to 2hi), but the goes back to 4hi... If I keep trying to put back into 2hi, eventurally, after many tries, it will infact go back into 2hi... and sometimes, when I go from 4lo back to 4hi, it goes straight to 2hi????... what's with that?? Anyone had this issue??.. my next step is to replace the TCCM... any opinions?

Thanks,
Oz