This was asked a while back and I for got who actually responded and here is their answer.

RPM
2130 comfortably low (fuel efficient)
2500 mid zone
3000 high zone (for cruising)



"As I lay rubber down the street, I pray for traction I can keep, but if I spin and begin to slide, please dear God protect my sweet ride." -Amen

56 Chevy 3100