I had low water pressure when other taps were turned on during shower time. I therefore re-set my cut-in/out setings and the pressure is sustained now. The problem now, is thatalthough overall pressure is better, when another faucet in the house is turned on, I almost completely lose water in the shower. My water tank is a "Southern" I beleive 15 gallon. My well is 150' deep. My pressure is set at 30 on and 50 off. I have a tire type valve on the front side of the tank, and when I put the tire gauge on it to check pressure, it's full of water. What would you suggest I do? Is there a bladder in this tank? How do I set the pressure?

 

The problem is your pressure tank is water logged, there are two types of these, one style has a bladder. the other is simply a tank. All of the old style tanks I have seen (non-bladder) are galvanized. and are not used anymore, the newer bladder style are painted,In our area anyway.
If you have the non bladder tank and its not leaking, Shut the system off and drain out the tank. If its a bladder style, the bladder (or diaphram)is broken. Replace the tank.
Plumber John