Hi Robyn:
Good to hear from you, plus it's nice to hear you are pretty happy with your new Rushmore. I have to admit, I've never seen a Rushmore, other then a picture. We don't have any dealers close by. I probably should put that on my to do list.
Sounds like it must be pretty comfortable.
It's to bad the AC isn't doing it's job, but like hunter11 stated, there is an issue with those units. If I remember right, the ducting isn't closed off on the ends and or the ducts aren't sealed where the registers hook in. If that's the case then I agree with Keith that going to a bigger AC won't solve the problem.
Hopefully everything will get resolved and you will be a happy camper.
enjoy that family get together.