I am losing water pressure when showering and using the washing machine at the same time. I have a well system that worked fine until yesterday. My holding tank pressure is set at 35 lbs. I just had the tank replaced 6 months ago. The well pump is fine.

Increase the cut out pressure setting in the pump control box. You're a little low. If you need directions on how to increase your pressure click on back.
Regards, Tom