If you are worried that your faintness could be pulmonary hypertension, you could ask to be evaluated for it.
As it happens, I've had faintness for decades, due to orthostatic hypotension, which basically means that when I stand up, my blood pressure goes down (instead of up). I'm also winded extremely easily and need to approach everything very slowly, but I do not have pulmonary hypertension.
Fatigue is just part and parcel of scleroderma and many other autoimmune diseases. Unfortunately, the fatigue can also cause worry (like, to try to figure out what is causing it, or lamenting what we cannot do because of it) and then the anxiety can cause worsened fatigue! It's quite a horrible catch-22, and one that all of us are vulnerable to. See Scleroderma Fatigue, which includes a video by Amanda Thorpe.
Perhaps its possible -- and bear in mind that I am not a doctor and have no medical training at all! -- but I don't know anyone with pulmonary hypertension who could walk for an hour or two, with no problems. It is often hard to even pass a six-minute walking test with PAH. I should note here that the six minute walk test is a bit dicey with scleroderma, because we can flunk it without having PAH due to other systemic effects of scleroderma.
What is absolutely fantastic is that you are actively researching your illness and learning everything you can about it! The downside of that is that we can scare ourselves witless in the process, so I find it helpful to pursue ways to relax and deal with anxiety as being just as important as learning about scleroderma and its symptoms. Especially because our anxiety can worsen the disease process.
Knowledge is power, but power can be used for good or evil. It's evil when it's worsening how we feel. It's great when its giving us reassurance (eventually) and confidence in our ability to work with our medical team, and our support system, to deal with this the best that we can.
In the beginning, that can mean reading and freaking out, then seeking support and input, and calming down. Later on, we tend to skip over the freaking out portion faster and easier, especially as we gradually transition to focusing more on the happy and fun and even silly parts of our life.