Chevrolet Repair: Brake issue, power brake booster, haynes manual

Question
Hi Steve,
I have a 1997 Full size 1500 Chevy P/U truck. Recently my ABS light was staying on after ignition but would eventually turn off after driving for a while. Now the brake pedal is very spongy and occasionally makes a weird noise while vibrating and seemingly losing braking power. I was thinking maybe I just need to flush my lines of the old brake fluid and replace w/new but after looking at my Haynes manual, I saw that there is a vacuum power brake booster and a hydraulic brake booster and not too much info in the manual as to diagnosis. There is plenty of fluid in Master Cylinder but I am assuming it is original as I have not changed it in the 2 yrs I've had it. Any advice as to what are the more common issues would be appreciated. Thanks in advance for your assistance

Answer
Unfortunatly ABS problems can be quite complex, the fluid is more than likely NOT causing your problem and there can be several reason why this is happening, this makes it hard to diagnose this way, my advice would be not to play with it, brakes are obviously to important, have the ABS system checked by a reputable mechanic, sorry I could not be more help, good luck