I have a 97 chevy z71 that is giving me problems shifting into and out of 4 hi and 2 hi. My mechanic took the xfer case apart and said that there is nothing wrong with the mechanical part of the case; it works fine. He also said that he took the xfer case and motor out of the truck, and it would shift on his table. He claims to have changed the control modules on the xfer case and in the dash. He now claims that the xfer case isn't shifting due to the motor being burned out. Is there a test procedure to check the motor's wiring to see if it's working and carrying the correct voltage?

He has already changed the entire rear end, because the yoyo that owned the truck before, had a rear seal break, and it let all kinds of water and mud into the axle and diff, causing all kinds of problems. I know he isn't lying about that, because I saw the mud in the diff housing. He claimed that the rear end was locking up, causing the xfer case to fail to shift.

Does his story hold water? Is there a way to test the motor?