Your pressure tank is probably OK!
Your tanks is probably OK! The lower pressure may be in the pressure switch adjustment. The no water at times is most likely that the pump motor is intermittent. That's an electrical or motor problem.
I'm guessing this is an above ground jet pump? Whether it's a jet or a submersible pump, I suspect you may have a motor problem! If it's a jet pump the motor switch could be sticking in the running position or it could be a bad starting capacitor. If it's a submersible pump with a control box the problem could be a bad relay or a capacitor. If it's a 2 wire submersible pump it may have to be pulled from the well. With any of the pumps the stopping of and delay of water could be the automatic overload switch cutting off. This tells me there is an electric motor problem somewhere?
This could require the services of a qualified pump service person with an amp meter and an amprobe. Probably not a regular plumber or a general electrician.
As far as the water pressure goes, without a pressure gauge near the tank it's impossible to know or compare the the pressure. It's like looking at an electric line and knowing the voltage without a voltmeter on the line.
Once you get everything going, I suggest you look into installing a Cycle Stop Valve www.cyclestopvalves.com. This valve will give you a constant pressure in your home and you won't get a variable pressure in the faucets or shower again. You're wife will love it!
Cycle Stop Valves also has a new product on their web site called a Pside-Kick. It's a package constant pressure system minus the pump.