It will be easier to grease with the weight off the suspension. If it won't take grease then, take the zerk out and see if you can squirt grease through it. If not, replace. If you can, you may have to use more pressure to get the grease in the fitting, or there could be something obstructing the grease in the suspension part which I would think would be checked out under warranty.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL