No subject

having trouble with an abs sensor a few weeks ago, similar symptoms to what 
you're experiencing, but when I turned off the abs the braking returned to 
normal. 

You did say that the parking brake light was on the whole time, maybe you've 
damaged the rear brakes and they are now not engaging except when you really 
step on it and even then it might be with a damaged pad or rotor.

Pull the rear wheels off and take a look at what condition the rear pads and 
rotor are in.

George Tur
91 V8