Idle air control valve?

Thanks for the replies,
Went for a drive with the trans tech guy and scan tool, there were no
stored codes (no surprise since the engine light has not come on).
Everything checked out normal except some fluctuations from the MAF
sensor in time with the RPM changes. But the torque converter unlocking
was the initial 2000-1600 RPM drop.  After that the engine
just..stumbles and hunts for a bit while you are coasting. I am going
to try cleaning the MAF I think, and see if that helps. I do know my
air filter was pretty much black when I changed it last.
As for the downshift clunk, again the scan readings were normal, but it
was confirmed the clunk/bump is felt and heard right at the 3-2 shift.
They have suggested dropping the rear driveshaft to eliminate the
chance its because of driveline slop (but i recently had it checked out
and was ok...) and driving it in 4wd to see if the clunk is still there
on the downshift. they agreed to try this next week. There is a 12,000
km (or maybe, hopefully, miles) 1 yr warranty on the rebuild (done in
March, 6000 kms ago). They seemed stumped with this and claim 4r55e's
do not generally have this particular issue. They are clearly reluctant
to drop the trans again to look for internal issues.
Tomorrow, hopefuly I am going to put the truck on a hoist and lift the
rear wheels up and get my buddy to hit the throttle until 3rd gear, and
then let off the gas and allow it to downshift on its own and
look/listen for the exact location of the clunk, assuming it will still
happen (it does when coasting to a stop).