Virginian - There are two things I would ask you to consider.
First, you are still "early" in your recovery. If I did the math correctly, you are about 2 months into things. It is still early. At 2 months, I was just beginning to feel like myself again. So, maybe a bit more time is warranted - regardless of how you felt last time, this time may be different.
Second, do you know what the settings are on your pacemaker? At least, what are the minimum and maximum heart rates programmed into it, and does it have its "rate response" functions on or off? Many times when they first implant pacemakers, they set them as if we are all very sick octogenarians, using very cautious low settings to allow the heart to heal and the leads to implant securely. Then at the first post-implant pacemaker interrogation (usually about 3 months after implant) they will discuss adjustments with you. Check your heart rate at rest and during activity. If it stays low, like around 60 beats per minute, then the pacemaker settings are probably keeping you down. If your pacer raises your heart rate in a normal fashion, going higher during activity, then it may not be at fault. Over the first 6 months or so that I had mine, we raised my "maximum" paced heart rate from about 120 BPM to 160, and turned the rate response on, then tweaked its timing. That helped me to be able to exercise and to live a relatively normal life.
BTW - A few days ago I received an automatic email from vr.org telling me that you had tried to PM me, but my mailbox was full. I've made room, and will watch for you.