"I greased my U joints this evening, but I could get much to even penetrate the zerk... weird."
Two thoughts:
1) they don't hold much grease - just a small hole down the length of each leg of the cross to allow the grease to get out to the bearing cups (also happens to be the outer race). The cups aren't that big & they are pretty full considering that they cover the needle bearings and the ends of the cross (inner race). Basically the only room for grease is the area around the needle bearings.
2) without regular service (grease) the bearings could have gotten hot enough to 'cook' the grease & make it harden. You can't force new in if you can't push the old out.
I had an old Dodge & the U Joints didn't have Zirk's. When I finally went to replace, guess what ... no grease in the cups & no needle bearings either - just rust colored dust.