I own a 2010 Ford F350 with a six for twin turbo diesel it throws a code P0088

Why does this only happen when outside temperature is above 65°F.

I'm afraid I can't say why that would be the case definitively; I can guess that it has to do with fuel controls prescribed based off of many factors including ambient temperature and barometric pressure. But that's merely a guess. The diagnostic flow chart is pretty thorough on this concern and can be followed with a good level of success.