Everything you are describing sounds like you have Hypertrophic Cardiomyopathy: Diastolic Dysfunction is the form of heart failure that this disease carries, unlike Systolic Heart Failure which is connected to Congestive Heart Failure. Patients with HCM have a real problem with shortness of breath and their heart rates tend to drop on the tredmill because the left ventricle cannot pump blood out due to stiff heart walls. The angiogram will show if there is any blockages in the arteries, it will also show how well the heart walls are contracting which is why they may actually be preforming the angiogram. You should do this test. If you have HCM, and I'm not saying you do, there are drugs (calcium channel blockers) that help to relax the heart muscle so the heart can pump more efficent. Many people live years with this form of heart disease, some do not and require transplantation.
With the shortness of breath you are having and the tests that you have took that show something to be not right, you should seriously consider the angiogram. The angiogram, where they go through the groin up into the heart and shoot some dye to look for blockages, is the most accurate test. If you have any blockages, you should know about it and try to get it fixed before it is too hard and a stent cannot be put in. Then, it would be heart bypass time. If you are able to walk on a treadmill, your heart must not be severely blocked. People who have severe coronary artery disease cannot walk on a treadmill. Females are at risk for blockage in the small vessels which is serious in that the heart muscle cannot get the blood flow needed. Some people grow new arteries to reroute the plugged arteries. Stem cell research and procedures that I believe are only done out of the country for now, should give hope to all people growing new arteries. For the time being, it would be wise and put your mind at ease to have the angiogram to make sure that there are no blocked arteries causing you to be short of breath. As far as your job, is there a way that you can get a different job where there is no lifting. Lifting is hard for people with heart problems. If your current employer does not have jobs that have no lifting, there are organizations that look for jobs for people 55 and older. It may not pay what you are making now, but you may feel better health wise and be able to spend less on healthcare. I hope you are feeling better soon. Try to get enough rest, eat right, and take your medication as prescribed by your doctor. Take care.