[vectorit]

What is the engine?
How do the spark plugs look?
Have you replaced the intake lately?
Have you inspected the water pump for a water stain - on a small block water pump there is a hole on the underside, and goes up to the pump shaft bearing. If it is showing a water stain or is wet, the pump bearing is going bad.
What kind of radiator cap are you using? If it is bad, it could be blowing steam through while you are driving.

I have had similar coolant loss issues in the past, and found that steam loss will cook off coolant pretty quick.