A couple of suggestions.
The first is to use a Phillips bit socket and use a ratchet. Doing it this way allows one hand to apply only downward force on the head of the ratchet while the other hand can do the turning. Much better than one hand applying both pressure and turning force.
The other...
One possibility is that grease has leaked past the grease seal (that keeps the grease in the bearing cavity) and dropped down onto the shoes. I had this happen once. It will lock the wheel hard. When you get it apart look for any grease on the shoes.
I had the exact same situation about a year ago. Mind you it was a totally different engine (Ford 2.3L) but my scenario was almost identical to yours. It was a cold morning (-20C or so). Car ran fine, drove it for about 20 mins on the highway. Got into town and was stopped at a light. I noticed...