You can pull the fuses that say 4-wheel drive, as a test. I think that there are 4 of them. The 25 amp one should shut off the servo motor. That shuts off the transfer case. We got a whole new transfer case but it didn't fix our problem.

I ran into someone, that had a 2006 automatic, & she had to keep her gas tank at least 3/4 full or it would hesitate, shudder, or vibrate.

Good luck!
Jack