It is a ECM/ABS issue because it monitors drive shaft speed and wheel speeds to control anti skid. Right now the firmware is pretty confused as to what is "normal". So reprogramming is needed to cure this.

 

Got the PCM back and installed along with 43lb injectors. It was recal'd for the 4.88's and injectors. What a huge difference, I am now very happy with the gears, this thing will light up the 35's well into 2nd gear now, and when the tires do grab the truck pulls instead of bogging out, it's sweet. The only weird thing is that it is reluctant to shift out of OD when I am over 70mph and I floor it, but if I pull it into 3rd manually it still has 2500+rpm's before redlining. Maybe the computer is still learning? Anyway, looks like my 1st impression was a just a little off, the gears are a little noisy but I was kind expecting that. I'm a happy camper now

 

Not work? Why not?

I have 342 gears and a PCM tuned for 410s. My speedo is off but my ABS works just like it always has. I always thought the ABS sensor in the hub just monitored the vehicle speed and checked if the wheels are locked up (thus engaging the ABS).

 

Some GM's do have a reluctor ring, but it is usually mounted on the pinion. The later trucks from about the mid-late 90's on had wheel sensors. I think it might be right around when they switched to OBDII, but I can't remember exactly when.

 

I think this is how it works. Theres the VSS (vehicle speed sensor) in the tailshaft of the tranny. This measures how fast the d-shaft is spining. Using the gear ratio programed into the pcm, it knows how fast your rear tires are spinning. The front is different though. Each wheel has its own abs/speed sensor. When you swap gears the pcm gets "confused", because the d-shaft/rear wheel speed doesn't match up to the front wheel speed, thus throwing the abs light. This is how it was explained to me by the shop that did my gears. It's very common for the abs light to appear while on a dyno too, because the back wheels are spinning and the front one are not.