If you are saying that your mph begins to decrease at the same time the shaking begins, then your cause might be a frozen front brake caliper, but this would almost always cause a pull to one side or the other. If it is just shaking and you are not 100% sure as to whether the speed is really being affected, then try rotating the tires front to back and see if the shaking goes away. Check the front end components for looseness also.

what happens is your computer sets a fault in the air compressor control unit and usually disables compressor operation until the code is cleared with a scanner or by running its self tests without any faults (could take 40 to 60 tests before the code will clear itself)the fastest way is to have the codes cleared to see if it functions normally afterwards.Also try to locate the compressor relay im unsure on this vehicle where it is at but if you can locate it try tapping on it and see if the compresor runs as your old compressor may have fried the relay.

Hmmmm, owing the fact that its air suspension. IT MIGHT, time to visit your friend neighborhood shop

Mine does the same thing. I press the tripmeter to reset it but it keeps coming on. I read somewhere that this is a dealer fix.

Have to check the suspension module for fault codes. I just got done with an 04 H2. Had fault codes and suspension error message. I am ver familiar with this system so if you can get someone to read the fault codes I can help. But I will tell you now that the pumps do go bad and if you have to replace the pump aka the air suspension air pump you then also have to buy a new air suspension control module that does not come with the new pump, even though the air suspension pump costs about $900. The module is another $290 about. Cannot say whats going on (nobody can for that matter) until codes are pulled. Standard cheap code readers cannot access it, only the professional shop grade $2000 scanners can like my OTCGenisys. I doubt they did anything intentional.

Here is a forum, hope this helps.

http://www.gmhummer.com/forums/showthread.php

Check power steering fluid if low then add accordingly, chack also the wheel bearing if worn, dry or damaged; replace.

cv joints if you got an open axle