Now back to trying to help Laura.
Here's what I believe is the manual for your water heater: http://manuals.adventurerv.net/Atwoo...er-Service.pdf
From my quick scan, it appears that it either has a temperature adjustment or is set at 140 but that can be replaced with an adjustable thermostat.
140 is quite hot however. I think you need to measure the temp of the water to seen if it's that hot. (Do that at the high-pressure relief valve so you know it's really the water temperature and not diluted by mixing.)
If it's 140 there, you might have a bypass valve set incorrectly, or you might have an open shower valve which is mixing the hot and cold
I think we need some measurements before we can proceed any further.