Checking to see if any other owners are experiencing low water when pulling from the fresh water tank. The toilet and bathroom does just OK. No way is there enough pressure to shower. The kitchen sink starts ok and then loses pressure. I opened up and listened to the pump and it sounds strong. Than noticed its only a 3 GPM. I just don't think that's enough hp to lift the water 8' to the shower head. Any thing I should check before I buy a stronger pump?