Diagnosis - The Symptoms

Nissan Frontier 2001 XE-V6
Drove 10 miles from home to school to pick up son - all fine.
Pull a U-Turn to pull up to school driveway and son jumps in.
As soon as we pull away something feels wrong, odd vibrations, engine noise all wrong, and when shifting feels like it is just grabbing. Hit 5th and notice the gear lever runs into the guide on the right hand side, the whole thing appears to be leaned over to the right. Holy cow…
Drove it gingerly to the shop and left it there…

Most likely, you have broken transmission mounts and/or broken motor mounts.
Get that credit card out, and prepare to charge away!

Verdict in:
Both engine mount retaining nuts were missing and the engine had “jumped” off the through bolt on the mounts! $100 to re-seat the engine and replace the nuts.

Now, how in the heck does that happen, and what was the engine resting on?

Are you the original owner, or did you buy this as a used vehicle?
Are you aware of the engine ever having been pulled for major repair/replacement?
It sounds to me like the engine was removed at one point, and it was not properly secured to the mounts afterward.

Good questions:
Purchased new.
No major work, no accidents of any kind.
No off-road racing, though I live in Hawaii and to get to some beaches the roads are dirt and some very rough.
I am not the most gentle of drivers, though nor am I abusive of the equipment.
Is there any type of non-major work that would require the engine to be lifted? Any recalls on this truck that would have required it?

got any “friends” that like to play jokes?