Post AX15 / T-Case Rebuild ??

So I did a full rebuild of my AX15 and swapped to an external clutch, and a full rebuild on my T-Case and added a SYE. 8* shims to get the pinion all lined up...

Runs like butter!
Super smooth shifting!
Rides like floating on air!
Idles at 500/600 ~ before was more like 750-1000.

There's 2 things I've noticed...
1. Speedometer no longer works. I don't know if it's a wiring issue or the different diameter of the RC output shaft

BUT MORE THAN THAT

2. Though it idles awesome (in neutral w/ parking brake on), it "goes to sleep" when I quickly come to a stop.
* Happens when I shift to neutral or use the clutch.
When the RPMs drop from 2000'ish to idle, they don't stop till she's asleep.
And she's running so smooth, I didn't even notice the first time or 2 until after a moment or 2.

Since it shifts super smooth now = I know the clutch assembly is working
Since it idles perfectly fine in neutral with the parking brake on = I don't think it's the idler shaft baring.

Everything ran the way it should before I did the work (minus the clutch slave or hydraulic line issues) so................

Any thoughts on what to look at/for?

My TPS and CPS are lifetime from O'Reillys
So I'll swap them for free and see what I see...

No clue what was up
Went under to finish up a couple spots and noticed where the trans support had snagged my temp band exhaust spot (where the front pipe and muffler mate) had come a little lose and there was some exhaust blow by.
So I redid that and drove to the parts store... No sleeping engine.
Drove it a few times since and no issues.
I can't imagine the blow by changed the back pressure (goes into 2.5" straight pipe) enough to cause the issue.
But since fixing that, the Jeep gods have smiled upon me and ...
She's good now