what can cause the 'ABS' and brake light on a 1995 gmc 3500 vandura to come on. At a slow speed the lights turn off then back on at around 20-25 mph. I haven't noticed any different braking power.
1995 GMC 3500 vandura 350
new master cylinder, or at least the front.
You will need to get the codes scanned, but I have seen this problem ocurr with bad wheel speed sensors. A scan of the system will point you toward which one it is.
20 years auto repair experience, ASE Master Tech, Mechanical Failure consultant, Expert Witness