Transmission noise

[hangun61]

My 96 Blazer, 4.3 4WD with 186K miles recently had a catastrophic failure of the rear differential. It was repaired (ouch) and has been fine for about 5 months of mostly highway driving.

Recently, within the past month or so, when shifting from park to drive, or drive to reverse, it has been making a "klunk" noise accompanied by a lurch that you can feel.

My inspection of the drive shaft and the rear differential found nothing obvious, so I removed the rear wheels and looked at the brakes and rotors. One of the brake shoes on the left rear was cracked, but other than that I didn't see anything obvious. While I had it up on jacks, I decided to start the engine and put it in drive to see if I could locate the cause of the noise. The left rear stayed put, but the right rear kept spinning until the brake was pressed down hard all the way to the floor. The driveshaft and universal joints all look and feel normal. (no play or distortion etc...)

I know I probably have a brake problem, but could this be the source of the transmission noise, too?

Anybody have any ideas or advice as to what I should look for to isolate and repair this noise? Any help is greatly appreciated.