Thanks for the added info Mike; I think we may have been talking about 2 different types of settling.
There is a period after construction where trim and framing lumber shrinks some as it reaches a lower level of moisture than it had originally, and it will cause the types of problems you mention, along with a few others like puckering horizontal drywall joints on 2 story walls.
This is likely to be what you're experiencing, but if the large gaps at the floor your seeing are primarily along one wall, I'd check the floor for plane by pulling a string end to end of the room near this wall at the floorline. If the floor sways up and down much below the string, you'll want to see if this wall is perpendicular to your joists or trusses.
Sometimes there may be a low spot that wasn't filled in the top of the footing or basement wall, which the mudsill and floor framing initially spans over, but can eventually settle into, and this will cause waves in the floor as the joists or trusses get out of line with each other.
If this has occurred, the trusses or joists can be shimmed back into plane with metal plates under the mudsill, directly below each truss or joist, on top of the footing or basement wall. Do not use wood shims for this, as they will not last long term. You'll also want to be sure and fill any voids you create under the mudsill from shimming, and I'd use a good flexible caulk such as BigStretch, or expanding foam does well, too.
I think that would cover everything; good luck & let us know what you find!