I found out after going thru everything that my fancy hose was the problem. Not enough flow with one of those clear plastic coiled things, that are supposed to stay off the ground and stretches to 20 feet etc. Only problem is they are maybe little bit bigger than 3/8 and wasn't getting enough flow. Flow was hard to tell except in shower, rest of RV little flow didn't show up.
Found that our after making sure all restrictors were removed. Wife says "we've tried everything let's change the hose and see what happens" I looked at her thinking to myself, ya right, look honey you can see right thru this fancy clear plastic thing, do you see any restriction? But to keep her happy I changed hoses. BIG EGG on my face. Other hose was bigger diameter and that made a difference. Not so much in the sinks, but at the shower head made a big difference.
(Glad I only thought what I was thinking and didn't say it.)