You have a bike with ignition points. Therefor the first thing to check for most performance complaints is the ignition dwell and timing. This particular complaint is often a small hole in diaphragm tho.
If points are right and diaphragms are right there may still be an ignition problem. I don't ever see may other riders report this but when a Dyna Booster went out on my bike almost ten years ago it got weaker and weaker in a couple of stages. It did not die all together at one time. I got some miles with poorer performance before it was completely dead. Then when I went back to stock points the bike was fine again. So if everything else looks and tests fine revert ignition back to points only to test if there is a problem with the Booster.