[BMERDOC]

It's probably fine at that speed. You don't need it so fast that it fights the brakes or so slow that it causes other problems. It's not a complete science. Personal choice for idle speeds vary between people by several hundred r.p.m. If that idle speed works for your truck then rock it. The next step would to be to check timing and idle mixture bit you'd need equipment for that. Some sort of tach, a vacuum gauge and a timing light should be considered basic tools but it sounds like you are fine where you are. If you wanna tweak the tune some more you'll have to invest in at least a vac gauge.