Tony
That’s good news. The deceptive part of riding at least to me when I restarted and to even a greater extent when I started equipping a touring bike is the effect of weight and climbing. If you feel you are 50 pounds heavier than your weight you remember riding at as a young man then you are actually carrying the weight of a fully loaded touring bike with you at all times. I read so much about touring cyclists shaving a few pounds here and there and I found it hard to believe weight would play such a big role. On the flats it really isn't much of a difference once the rolling resistance is overcome. But throw in a 3% climb that looks like not that much but you are slowly lifting that weight up against gravity and it is a big deal. Getting the oxygen into the muscles can quickly reach a point of demanding more than you can provide. Feeling that coming on and adjusting to it can be big. I find things like you asked about in your first post play a big part in it such as allowing your lungs room to expand etc. I also find that as I get older the time between eating and exertion has to be greater. As a kid I could eat a lot and go jump on a bike and go full out no problem. now I do much better leaving a few hours in there or eating more lightly and often if I'm working hard. I don’t know why that is but in my case I have found it to be true.
All the advice about a professional bike fitting is good. I am a person that like to see cause and effect. And it might be a slower process getting it right doing it yourself but when you do get it worked out you will know what to start changing again as you lose weight and want to make your posture more powerful again. Things like an adjustable stem are great places to start and as you improve can be changed easily. Keep us involved in what you do and thanks for being so open about your problems.