Weapon Equip Slots 3 & 4?

[Jurassic Fart 1]

I've already rescued Roland, and haven't unlocked a third Equip slot yet. When, exactly, does this happen? I'm running through the second playthrough on TVHM, and can't remember when the third and fourth equip slots are unlocked. Sure, you can use Gibbed to illegally unlock these slots, but then you run into the infamous "Can't Touch This" glitch; if you illegally unlock equip slots, you run the risk of screwing up your backpack access AFTER passing the legitimate unlock hurdles.

I'm playing legit, but I'm getting REALLY tired of having only TWO measly equip slots. Where are those ♥♥♥♥♥♥♥♥♥ third and fourth equip upgrades? I'm getting close to the end, and I have no ♥♥♥♥♥♥♥♥♥ clue.

[Draekus]

weapon slot 3 unlocks in NVHM with Plan B mission

weapon slot 4 unlocks in NVHM with Bright Lights, Flying City mission