99 Trail blazer, 250k miles, regular maintenace.
I had trouble with Abs last winter and ran across the many threads discussing the low speed activation issue and the solution.
I found the wire to the front right wheel sensor was broken and repaired it
and all was well. I measured both front wheel sensors with DVM and got readings that were acceptable.

This winter the abs started acting up again, ABS light was lit. I measured the front right and it no longer gave readings with spec, so I replaced it. ABS light went away. I am still getting the low speed activation symptoms. Both front wheel sensors give voltage readings within spec.

When I test the brakes at a higher speed on a snowy surface the ABS system works fine. But on a dry surface at low speed the ABS activates and I can let off the pedal and then re-apply and it seems to work fine.

What would you recommend as the next step or steps to diagnose this problem?

 

You're getting low speed activation.

I found this information below. I think your problem is the air gap from the sensor to the reluctor. May also be a worn bearing causing a gap larger than the tolerances allow for.

The information below will show you how to troubleshoot your front ABS and determine where the problem is before you go out and buy a new hub. Here is how to troubleshoot it:

1. Remove both wheels, remove the caliper, pull the rotor, unplug the speed sensor, hook up a digital meter to the speed sensor plug, spin the hub by hand. If you don't have 300mv AC or more, go to step 2.
2. Remove the speed sensor screw, clean the sensor real well as well as the mating surface, reinstall and measure your voltage, if less than 300 mv AC go to step 3. This where most people would buy a hub... don't do it yet!
3. remove the speed sensor again and look at the mating surface. You may not realize it at first, but the mating surface is a stainless spacer that is held to the hub with a rivet, hit the bottom of the rivet head with a chisel but don't try to cut it off, doing this will raise the rivet and you will eventually be able to grab it with vice grips and pull it out and release the spacer.
4. stuff the sensor hole with a torn off piece of paper towel and flat file the surface to make it clean and smooth. Clean the stainless sensor and make sure that it's flat, I put mine on a flat surface and rubbed it flatly on fine sandpaper to clean it up.
5. put a little waterproof grease on the hub's sensor mounting surface and a little on the O ring that is around the speed sensor and reinstall.
6. check your voltage *********** CAUTION.... DO NOT leave the stainless spacer out!!!!!!!!!! ********** Failure to reinstall the stainless sensor will result in the wheel sensor being too close to the reluctor wheel and it will break a tooth on the reluctor wheel and destroy the speed sensor as well. If you break just 1 tooth on the reluctor wheel, your ABS will fire on EVERY REVOLUTION of the wheel!!

IMO, people are replacing their hub before removing the spacer and cleaning the surface underneath. This easy procedure will keep you from replacing a hub when it's not required and will give you a good idea where the problem is coming from by reading the voltage. My sensor jumped from 125mv before cleaning to 800mv after cleaning the hub surface under the spacer!!

Here is the TSB info courtesy of Maniac Mechanic:

The spacer is used to provide a proper air gap between the Reluctor wheel and sensor if you still have it reinstall and see if that solves the problem you are currently having. If that one goes away and you still have the original problem this is GM' s TSB on how to fix. Brakes - Low Speed (Below 5 MPH) ABS Activation
Notes

Bulletin No.: 02-05-25-006B

Date: January 05, 2006

TECHNICAL

Subject:
Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)

Models:
1999-2000 Cadillac Escalade
1995-1999 Chevrolet Silverado (Old Style)
1995-2000 Chevrolet Suburban, Tahoe (Old Style)
1995-2003 Chevrolet Astro Van, Blazer, S10
1995-1999 GMC Sierra (Old Style)
1995-2000 GMC Yukon, Yukon XL (Old Style)
1995-2001 GMC Envoy, Jimmy
1995-2003 GMC Safari Van, Sonoma
1995-2001 Oldsmobile Bravada

Supercede:

This bulletin is being revised to update the correction and warranty information. Please discard Corporate Bulletin Number 02-05-25-006A (Section 05 - Brakes).

Condition

Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause

The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

 

The sensors are fitted, & shimmed if necessary, during the manufacture of the hub & bearing. Not recommended to replace just the sensor, for this very reason.

 

I had found the above info too. Quite helpful. I did all the steps and voltages from both wheels were within spec, so the Abs system should operate correctly.
When it still exhibited low speed symptoms, I posted here thinking there might be something else to check. I guess for now I will monitor the symptoms.

 

one hillbilly way of finding out which side is doing it is when you are braking under 5mph take your hand off the wheel which ever direction it pulls when the abs activates, its the opposite side that is giving you issues. so if it pulls right then its your left one activating . everytime we ran across this at work we would pull the sensor out and lightly grind down the mounting surface so its nice, shiny, and smooth. dont get too crazy grinding it just knock all the rust off. slap some grease or anti-seize on it and away you go.

this also happens to dodge and ford, pretty common but the cleaning of the surface area always fixed the problem if you can actually get the sensors out which you said you did.