2002 GMC C1500 trans?

Leadfoot33,

This newer truck may be giving you a problem that wasn't found on older vehicles, like you said. The first inexpensive thing to try is cleaning the mass air flow sensor. The vehicle shifts according to engine load, vehicle speed, temperature....and on. If the sensor becomes coated an improper data stream reading will change one or all the shift points and feel.

This sensor is mounted to the intake tubing right after the air filter.

It can be cleaned with a sensor safe solvent available at an auto parts store, by spraying several shorts bursts directly onto the element. Simply remover the air filter top from the housing and then the air ducting it clamps onto.
Once the sensor is cleaned the PCM (engine computer) must be reset either with an automotive scan tool that can reset the transmission adapt, or simply remove both battery cables and connect the two loose terminals together (don't touch the battery!) with a conductive material like a screwdriver for about 15 seconds.
The initial ride afterwards will feel different regardless if it corrected your problem and will need a couple days to relearn you driving habits.

Good Luck

The most common symptom of a bad wheel bearing is the noise in one direction but not the other but is more noticable at speeds of 20 - 30 mph. Moving back and forth in your lane will also simulate the conditions for it to act up. Make sure there are no cars near you when you try it.

Also, have your guy inspect under the vehicle for any parts rubbing the tires, like a loose fender well, before you condem a bearing.

Good Luck.

I believe I have your answer. Since your first post the noise is now additionally being described as " œgrinding.' I am willing to bet if you drive near a wall below 20mph you will hear the noise emanating from the rear if you have the windows rolled down. Based on your mileage the rear brake pads and parking brake shoes, (inside the rear brake rotor), need to be inspected and probably replaced for the first time.

You've probably heard it before, but that grinding is the lack of brake pad material contacting the brake rotor, or " œmetal on metal' as we call it. With the rear pads it usually starts out as an occasional grind/growl when turning when the vehicle is being driven for the first time in the morning. After warming up, the noise usually dissipates; until some time passes and the rear pads become so worn that the noise becomes constant and is better described as a grinding.

Get the brakes checked out, front and back, first and please post back as you get updates or need additional help.

Good luck.

I will be the first to admit it; we have made this mistake in the past. It gets so busy sometimes at the shop we glance at the brakes instead of thoroughly inspecting them.
When the truck is on the lift, ask to see the brakes yourself and take a close look at the inside pad on the rear passenger side as it is usually the first to go.

In the mean time try setting your parking/emergency brake. Does it seem to go all the way to the floor? The components that make up the parking brake require more disassembly than simply taking off the wheels and tires. If you have the symptom above they need to be inspected.

Please post back if the problem is not solved or if you find the solution.

Good luck.

Perhaps it's not a coincidence. This model year, though more common in the 4X4 styles had a string of the Electronic Brake Control Unit (EBCU) failures. The symptoms were a growling noise on all the time even at stops with the vehicle in park and sometimes the key turned off. Does the noise you have been experiencing sound like the ABS is activated like if the vehicle were sliding? If so the ABS module requires replacement.

These are easy to replace, but depending on the area you live in could have some corrosion on the small bolts holding it in place. Just be sure you have the torx socket straight on with the bolt and twist with firm even pressure. It is located on the drivers side under the vehicle tucked next to the frame rail just behind the drivers seat on the inside of the frame.

Be sure the ignition switch is turned off before starting. Once you have it out the vehicle is okay to drive, just cover the hydraulic unit on the vehicle with tin foil. The repair will cost between $130 to $700 depending on which one your vehicle was equipped with. Some styles can be sent in for repair in just two days at an inexpensive price. If you have the non repairable style the dealer has many in stock to put on the same day at the more expensive price.

REPAIRABLE UNIT

Connect to this site for rebuilding your module if applicable, for contact and mailing information.
http://www.modulemaster.com/en/services/index.php

Please post back if you require further assistance or find a solution to the problem.

Good luck,