Watch the Practice: Speed & Stamina online guitar lesson by Cathy Fink from Bluegrass Rhythm Handbook

Bluegrass songs and tunes come in all tempos. When you're building your speed, take your time; use a metronome to practice and don't go faster than you can while staying in time. I guarantee that a few days/weeks of practicing like this will serve you very well later on.

Speed takes a good sense of timing but also stamina, which takes a little time to build. Be patient!