I need some help gentleman. In the last 2 weeks I've noticed my wife's 07 Burb running at little higher RPM than normal (300-400 higher @60-70mph). I've also noticed a low pitch/dull hum. It almost fees like it's in tow mode, but when I manually engage tow mode it clearly shifts into it, then out of it when I disengage. It has thrown no codes. Transmission ran at a cool 174 degrees on a 2 hour trip at highway speed yesterday. No apparent vacuum hose issues. New air filter. Any suggestion on what I need to be looking for. Thanks fellas.

 

May not be shifting into OD? Miles/history?

 

no, over drive would be more than 1,000 rpm difference at that speed. its unlocking the torque converter for some reason when not in tow... that is weird...

 

135,000 miles. No previous issues. Dealer serviced @75,000. It is shifting into OD.

 

Just somethings you might check.

Have you checked the brakes could be one of the rear brakes dragging.

Has the rear diff been serviced or checked. The dull hum could be the rear diff.

Something could be caught around the drive shaft, not that likely as there would be some vibration but something to check.

 

Thanks for the replies. Let me paint a little clearer picture. 2WD 2007 Burb LT. I drove again today on a 100 mile round trip. I still feel like it's running a higher than normal RPM. 300-400 rpms higher. There is a dull humming. A slight but noticeable vibration in the steering wheel and floor board. When acceleration takes place you notice the whine/hum and vibration increase as well. When you take the foot off the gas and begin deccelartion you notice an "unwinding" feeling in the vehicle. While in park and getting the rpm's up there is no apparent hum/whine. It only happens when in drive. Keep on sending me suggestions to look at. Going to the dealership is a LAST option only. Thanks for your input

I have not had the rear diff serviced.

 

Bit of a long shot, but it could also be the catalytic converter.

 

I appreciate Bluedog. Making a punch list that I'll start on this evening. Would a U-joint give those symptoms?

 

I would revisit the vacuum leak checks... you said new air cleaner... did the problem start after the air cleaner or was it there before?
Check all connections along the air intake snorkel...
Did you disconnect the throttle body in any way? If so it could be in a relearn mode and the RPM's will be a bit higher...

 

in2pro, air filter was replaced in late Dec. This issue started a couple of weeks ago.

Speaking of vacuum hoses........

The symptom I'm experiencing on the burb is almost like a shop vac that's got something lodged in it but not clogged....still works, but working a little harder.

Nothing done with the TB

I appreciate your input in2pro. Keep em coming.