Feels like a 5 speed auto
 

Hey everyone,new owner of a 06 2LT 2.4 w/ auto with 63k.Thanks in advance of any help you can give. I love my HHR except for one issue that is giving me concern. When accelerating lightly,1st and 2nd are normal,3rd revs till about 3k+ /- and then drops down to 2200 then revs up to 3k and shifts to 4th.Feels just like a 5 speed auto. The heavier on the pedal the less drop in RPMs. Does not seem to do this much when engine is cold. This concerns me more. This also happens SOMETIMES(no pattern),there is a rather large fluctuation in RPMs(300-500) when in 3rd gear after the drop off and occasionally in 4th at low RPMs. At first I thought this might be an ignition or fuel issue. Cleaned plugs,injector cleaner,new high flow air filter but since this only happens in 3rd(sometimes 4th) I have a sinking feeling this is a trans. issue I don't even call mechanics, I come here first. Thanks for your help.

Sounds like your converter lock up isnt holding..wont notice this when cold because it doesnt kick in until water temp gets above 160...could be the solenoid..lockup will occur between 40-45 mph..if your around this mph it could bounce back and forth if the eng loads change alot, especially if the throttle is depressed more then normal cruise settings.
not sure about the 800 rpm drop off in 3rd...could be a sticky valve body causing all this.Any idea how it was used before you got it? May just need a good flushing and new fluid.

It could be in the 40 mph range since I am half way into 3rd gear at the time. Fluctuations will stop under heavier accelerations. Under good acceleration the fluctuation in the RPMs stop and the drop off in 3rd becomes like a normal shift whereas at light throttle it drops off like an overdrive shift. Not sure on past history but it is in excellent condition. Any idea on cost of trans. service? Thanks

Flush & fill runs around $120. A decent trans shop should do a free test drive/diag. AAMCO might depends on franchisee. Could be the TCM (Trans Control Module), there has been a spate on the forum lately.

On my chevy express van, I had the overdrive kicking in and out of lockup. Turns out it was the camshaft position sensor.
I would get a code reader to see if you have a sensor somewhere out of range....

It feels like overdrive kicking in but I'm only in 3rd and I don't believe this has an overdrive.

4th gear is "overdrive" on a 4T45 trans., if you didn't already know that. It is a 4 speed auto.

Just to be clear for everybody.

In fact, if you look in the 2006 owners manual, pg. 2-28, the position (D) is referred to as AUTOMATIC OVERDRIVE. Also, when the engine is cold, the transmission will stay in third for a longer period of time to aid in warming up the engine.

I read it at jury duty but I must of missed that. Thanks

I also noticed than when the RPMs are surging my MPGs are down 3-5 MPG. You can feel the car chug a little but not much. Almost like the trans is slipping. How can this happen only in 3rd and 4th gear. I will get trans service but was hoping for other things to look at and get them all done at once. I want to be informed before I take in for service. Thanks in advance