I changed out the expansion tank about 3 weeks ago and everything is working perfectly now. The T & P valve is no longer releasing water and the internal water heater pressure doesn't go much higher than the incoming water pressure. The old expansion tank was completely full of water. I'm not a professional plumber and couldn't have done it without everyone's assistance! Thank you so much for your help!
Sounds good. I came too late, but I had the exact same problem as you and it was the expansion tank and I was going to recommend pumping air into it to match your street pressure like you did. I also find that a good way to check the expansion tank is to flick it with your fingernail and listen to the sound on both sides of the diaphragm. One side should sound solid(filled with water), and the other side should sound hollow.......if in good working order.
One other thing I would do is install a ball valve on the line that feeds the expansion tank so that you can simply shut it off and throw a new one in without touching anything else. I'm sure some people wouldn't like that idea here, but for your own house, why not? I do the same on my boiler expansion tank and also I do it on the air scoop vent with a ¼" valve.
........now if I could only get a recommendation on my thread lol.