My 2004 sierra denali vibrates or feels like I'm running over the lane change bumps on the freeway. What could it be? The rear end, the transfercase, or the drive line?

Are you talking about the HVAC SYSTEM? If so, there are 3to 4 in front , same with rear if you have rear air option. They have different part numbers too.

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Switch has high failure rate. If that's the one mounted on the left side of the instrument panel.

the front wheels may need balancing or it could be a loose or worn tie rod end or other loose component on the front end, you will need get under the vehicle & have a good look & give the steering components & anything else a good shake to see if you can see anything loose or worn.........hope this helps......cheers.

02 gmc sierra denali making a vibration noise about at 50-60 mph slower speeds no noise.please help

change the fuel filter then get back to me.

check brakes, there is a tab of metal that tells you when its time to change brakes

This is the same as a check engine light or an ABS light. All three systems have their own computer and the ability to store error codes. Once in a while all you have to do is hit a bump and a code is stored. I'v been driving my 2004 Denali with this situation for over two years. If you don't feel ANY changes in the steering, braking, or the general conditions of driving than you've got nothing to worry about. If you DO feel a change in any of the above, then have the vehicle serviced asap. Thanks, Dana

If it is a problem that shows its self as speed increases as a constant shaking and on all types of road surfaces....it could be a wheel balance problem.

gas pump get somebody to start the car get a hammer and hit the gas tank under it normaly if it gas the electrical pump start with the shock of the hammer if it run you got to change that pump because its not gonna run for long let me know thanks for the post