So, you regreased the hub, you don't mention the freehub. There is a difference. The bearings in the hub aren't the same as the freehub. Pull the freehub off the hub, pull the seal (O-ring) off the spoke side of the freehub and drip in some synthetic motor oil, I use Mobil One 5-30wt, drip in all you can get it to take. You just need some thinner lube in the FREEHUB.

I ride in below zero (F) and have no issues at all after doing this on 6 bikes, my wife's and mine. BTW, I'm using Shimano and Chris King hubs, Campy may be different. Park tools website can walk you through the procedure to remove your freehub. I'm sure this will end your problem.