2002 Blazer, No Reverse.

[Brokecelebrity]

This is a further development on our Blazer that had problems with 2/4WD.
It got stuck in 4WD last month, had a couple diagnostics done on it, ran down everything I could, then took it into a shop.
Now won't go into reverse!
I found a local shop that did a diagnostic on it.
According to them, the transfer encoder was good, it was the TCCM module that was toast.
There are three versions of this for the Blazers, he ordered the 7 pin unit and schedule us for a repair.
I dropped it off yesterday before work, asked him if it would be done today, he said it should and I would be able to pick it up after 5 o'clock.
I got off work, walked down to the shop, it turns out his supplier had sent the wrong unit, they discovered this AFTER they had the truck up on the ramp and taken apart.
He said once they discovered they had the wrong unit, they bolted everything up again, took it down, called their supplier and explained the issue with them, and said once they had the right unit, they'd fit us in for the repair.
I backed it out of the parking lot, drove home with one stop at the store, got home, tried to reverse it into the driveway, all I got is whining in the rear and no movement. I put it into drive, headed up the block, turned around and nosed it into the driveway. I tried again to put it into reverse, same sound, whining or whirring, you can hear everything turning, but it's not engaging.
It COULD be a coincidence that the reverse went out right after the TCCM did, but what are the odds?
Any way the shop could have missed hooking up an electrical connector or vacuum line that would cause this?
The truck only has 81k on original transmission.
Any info appreciated.

[old_master]

What problem are you having with the 4WD? Does your 4WD switch on the dash have 3 buttons or 4 buttons? The TCCM and the encoder motor cannot cause only reverse to fail. If there's a problem in the transfer case that causes reverse to fail, forward gears will not work either. Have you checked the transmission fluid condition and level? How many miles since the transmission fluid & filter have been changed? Fluid & filter on the 4L60E transmission should be changed every 36K miles... if you want it to last