After some grinding, I head back to The Lost Cave. Being on par with enemies in terms of level made very little difference - but I was at least able to clear the caves, get some more quests out of the way, and move on.
Disclaimer: Borderlands is a game developed by Gearbox Software (with some other work done by Demiurge Studios, Shadows in the Darkness, and Darkside Games), and published by 2K Games (NA/PAL; Microsoft Game Studios and CyberFront for JP; and Feral Interactive for Mac). I do not own, or claim to own, any part of the displayed content - this video is for entertainment purposes only.