Questions like this challenge and "Has anyone...?" almost always can be answered positively. Here are two QX for June. July is more of a challenge, but U is available PDX-DFW on mainline AS 652 on 8/1, as well as 3/4 SEA-DFW flights on that day.
NB. AS is adding mainline service (A320) back to SEA-DAL in July. No U yet on the random days I checked.
