I'm not familiar with the '01 system but if there isn't a load sensing device that could be modified, then you have to change the bias by changing the proportioning valve effect. If you want to increase the rear braking, you need to remove the proportioning valve and install an adjustable unit. To decrease the rear braking, add an adjustable proportioning valve inline.
Before you go down this road, be absolutly sure that the rear brake system is functioning as it should. Your stock valve may be bad.
Be forewarned: As Dane stated "You have to be very carefull changing the rear brake bias. What works great in the dry will have you swapping ends when the pavement is wet. You'll never know you have a problem until a hard/panic stop in a corner, then it's too late. "