AT NORMAL SPEEDS THE TRUCK IS FINE ITS WHEN I SLOW DOWN ALMOST TO A STOP BUT THEN PROCEED IS WHEN IT OCCURS THE CLUNK SOUND.

SOURCE: heater core on a 2003 Chevrolet pickup 4 wheel drive crew cab

if you have air conditioning you will need to take it to a garage and recover the r134, you will need to remove the dash to allow you to remove the heater box, it's an ugly job, I've done a dozen or so and can do it in about 6 hours now, the first time it was closer to 11 hrs, good luck

SOURCE: I have a 2001 Chevy Silverado 4X4 Crew cab. 8.1

yes the front sensor will collect metal shavings causing this same problem.however you need to have it scanned when the lights are on. auto zone scans for free. the front sensors are in the front hubs. replace as a set as assymblies.

Testimonial: "Very helpful"

SOURCE: 2005 GMC Sierra 1500 crew cab - speedometer not working

This is a well known issue with model years 2003 thru 2005. There is a chance GM will replace it under recall... Call the Chevy Customer Assistance Center 1-800-630-2438 to find out.

If not and you want it fixed, try Southern Electronics at http://www.instrumentclusters.com/.

SOURCE: I HAVE A 2000 CHEVY SIVERADO 1500 2 WHEEL DRIVE

I agree with Jaisen23. Most likely warped brake rotors causing this, especially if the surging or shuddering ceases when you release the brake pedal. Worn tie rod ends or other steering parts can increase the effect so have those parts looked at too. Good luck!

SOURCE: when drivingtruck in 2 wheel drive the 4 wheel low

Sometimes the solenoids will stick on the axle neither in 2 or 4 wheel drive, if this problem started when you weren't shifting between two and four wheel drive it is probably the push button switch cluster on your dash going bad