This is funny, I just have to say something on this thread - I did the same thing. I hiked Baldy one month before Whitney as a practice, with a pack. I took the Ski Hut trail and, get this, stopped about 1/2 mile from the top. What a stinking steep trail that was. I think I had a bit of altitude sickness! Well, this really worried me with Whitney coming up.
I'm happy to say, however, that Whitney was no problem. I got to the summit August 5 with no sickness problems at all.
I just don't get it...
Good luck with your hike!