I followed that route last year solo from July 29 to August 8th. See trip report here:
Onion Valley to Whitney via Junction PassJust to add a couple caveats: trail was snow free; however, having said that, I am not sure how easy the route would be in May...... but having been through the area, I would not have a problem staying on or near the trail if it were under snow; however, my skill set would prevent me from going that early.
Before going I googled "Junction Pass" and "Shepherd Pass" and found a few pictures and trail reports. One report that I found was inaccurate (the trail does pass within a 100 meters of the first of 2 upper lakes..... that's were I camped the second night). Also, one report said that the trail drops into the canyon after the Pass, but in actuality it stays above (I suppose that the reason the report indicates that the hiker descended to the gulley was probably due to the snow conditions at the time) As I descended the canyon, approaching Lower Pothole, it was really evident where everything was, I could even see the Shepherd Pass trail as it passed by Lower Pothole.
I had previously been over Shepherd Pass many years ago so once I saw the trail; I was in known country again.
Once obtaining Shepherd Pass, continue cross country and take Rockwell Pass over to Wright Lakes then travel Wright Creek down a very beautiful canyon until you hit the JMT.
I hope to do this route again soon since it was both exciting and picturesque.
Paul