Just rode EWR-IAH yesterday. (I don't commute - was visiting Yankee in-laws

)
It was as full as it gets, with every seat filled, j/s included. I could have gotten on with a pass, but the crew let me take the 2nd cockpit j/s to get one more on in the back.
I used to commute as a new-hire, and summers were always the worst, load-wise, but even then I only got left off once or twice.
Two-legging is usually a sure ace-in-the-hole, since a lot of XJT flights carry through an outstation with the same aircraft and crew between EWR and IAH, probably a half-dozen or so every bank of flights. DAY, IND, CVG, BNA, MEM, TYS, GSP, CAE, SDF all have frequent service from both hubs.