Looking at the tech-specs for the Thunderbolt: http://www.lg.com/us/monitors/lg-34UM95-P-ultrawide-monitor it seems that the monitor only has an sRGB gamut, so it would be ok to use sRGB for output and viewing, I'd think.
I don't know how a Mac works, as I have Windows, but I'd suspect either the display profile is wrong, or it is incompatible with LR. Can you provide an example DNG which is your raw with it's settings saved to it, so others can try? You can use http://www.dropbox.com and include a public download link in a message. If you're not sure how do provide a DNG with settings saved to it, then maybe provide a raw file, and then a screenshot that has just the Auto Tone applied, and a screenshot of Develop and another of an sRGB Export in Finder, to compare with.
When someone else tries your same file with your settings, I expect it'll either look like your exported file, meaning the LR view is bad, or look like your LR version, meaning your Finder view is bad.