Wow, this troubleshooting really is something, eh?

So, this is a long shot considering all that's been done and checked...but the front diff mounts to two brackets (one per side) that each have two bushings, and those brackets are then mounted to the unibody. If you've still got the front diff off, you can grab the diff snout and move it up and down. I really can't imagine those failing, to be honest, but seems like the last hope.

What about the bushings on the control arms, or the steering rack mounts?

OMG - reading this 3 1/2 year old thread was like pulling my own teeth with a pair of needle nose pliers......and then it just stopped!

I went through EVERYTHING this guy did and finally, an old mechanic said
1)"put it up on a rack,
2)put in 4 wheel drive
3) put it in gear.
4)let off the brake and get the wheels turning at idle
5)put on the brakes!

And the front differential jumped forward.

The whole problem was the front differential mounts went bad.155,000 miles maybe soaked in oil.
$32 part, 15 minute to put in an my QX4 was as smooth as glass 0-85

What a PITA
Wow