After reaching level 50, I went into Moxxy's bar and gave her 10 1K tips. She have me a corrosive LVL50 submachine gun called something like 'Moxxy's bad side'. did about 3K damage and did about the same in elemental effects. A few sessions later, I did it again, and was given a weapon called 'Moxxy's good side'. 4K damage per shot submachine gun with fire elemental effects.
Thought sharing this would be helpful.. Good luck.