After 600 miles, I just check my tire pressure for the 1st time. All 4 tires were at 29.

I think the dealer must have messed up. I just filled all to 33 and the car drives much better.

Could the tires have lost 4 pounds in just 3 weeks?

I have a 2007 MCS w/ the Dunlap runflats.

 

Depending on where you're at and if it's been chilly? Yes!

 

Too many factors involved to be definitive. Temp is a big factor, time is also among other things.
Could also be the dealer set them to 29 to soften the ride since the runflats are so friggin hard.