Follower upgrades!

Followers can range from Uncommon to Epic and while some followers are guaranteed to be Rare or Epic, the only other chance you have is to hope you get a lucky upgrade when you first acquire them.

Wrong!

Leveling from Uncommon to Rare

It might not be clear from this picture, but once your followers hit level 100, they continue to earn experience from missions. So even if you get really unlucky with bonus rolls on followers, you can eventually get all your followers up to Epic anyway. It takes a lot of experience though. You can see that Mulverick's experience bar is about 1/3 full. The guy who just leveled up to Rare had a special ability that increased experience earned by 35% so he leveled up pretty quickly.

In addition to upgrading rarity level, once your followers hit level 100 you can actually upgrade their gear! You can get some of these tokens from doing missions with your followers:

Uncommon is 3 ilvls, rare is 6, and epic is 9. You can also find the weapon/armor upgrades themselves from salvaging the crates you get if you have a Salvage Yard. You can get some really nice enhancements this way, even as high as this:

The crazy thing is that these enhancements stack. It seems like they only stack if you do them in a particular order though. For example, if you start off by using an Uncommon enhancement (+3) and then use an Epic enhancement (+9), you'll end up with only +9 overall. However, if you do the reverse, you'll end up with +12. I'm not sure if it's as simple as a larger one will overwrite a smaller or if there is more to it.

It's also possible to find re-training certificates which allow you to re-roll the Traits/Abilities on a follower. I've only found one (and already used it; in retrospect perhaps I should have saved it for an Epic follower) so far and I have heard they are pretty rare. They do re-roll all of the traits/abilities, so you cannot pick and choose ones you'd like to keep.