Originally Posted by
customsound79
I'm usually in the highest gear possible to keep momentum because my legs are strong but not very fast.
This sure sounds like a cadence-related problem. Pick a gear that lets you turn the pedals at 80-90 rpm, and if your speed changes you should shift gears to maintain that cadence. Riding in high gear everywhere will unduly tire your leg muscles and probably cause knee problems if you do it enough.