Normally there are two causes for low water pressure, assuming good pressure from the faucet.
1. Dirty filters
2. Dirty screens
Since it's a new to you coach, I would find and replace all the water filter in the coach. Be sure to look under the kitchen sink. Next, where the water hooks up to the coach, look inside the one way valve...there should be a small screen with a washer on it. These get gummed up with all kinds of junk. You get 3 for 4 bucks at WalMart or you can by a 6 pak at Home Depot. Also, check the screen in your shower wand. Finally, remove the water saver washer in the wand too.
My guess, since you said it is low with your pump too, is your water filters need to be replaced, but if you're going to do that, replace the screens as well...Dennis