I got my Chocobo (Buster a Healer) to Rank 3 with just killing boars near Quarrymill while getting HQ Boar skins for my blacksmith guildleves. spent maybe a solid 4-5 hours out there and only got him to rank 3 definitely slow. I wonder if it would be much faster in a party of 4 with all chocobo's out. Also I noticed with my chocobo companion that when he got the killing blow no loot drops. I started my own thread about this possible bug.