My 2011 378 has the same 5500 onan. Runs everything at the same time with no problem. 2-13.5s in my unit. The only problem I have is that with both ac's on, traveling down the road, the transfer switch shuts off power to everything especially during drive over very rough roads.
Called Parallax and asked about the ATS 501 transfer switch in my unit, and the gentleman said that this switch was not designed for a moving vehicle such as a motorhome. For fixed installations it was fine, but extreme vibration would cause it to turn off power. If that is the case, G-town needs to look at another brand that is up to the task!
We are still extremely happy with our unit, and April Conner has helped get all the problems fixed. I only wish the overhead front drop down bed had been available when we bought our unit from Lazy Days.
Paul and Rosemary
2011 Georgetown 378 Firemist
2010 Jeep Liberty Limited 4X4