I have a 2006 Chevy Malibu MAXX with 122,000 miles. It lags when shifting from 1-2 and 2-3. RPMs go up to 3200-3700 depending how much throttle you are giving it. When it does go into the next gear, it shift hard almost as though it had a shift kit in it. Once it engages it stays engaged and does not slip. It downshifts properly and 3-4 don't seem to have the same issue. I just changed the trans filter and filled it with Dexron VI. It called for just under 7 quarts which is what I put in, and fluid just seeps out of the check plug. The shifting issue was there before I changed the filter and hasn't changed any since. I was going to check the shift solenoid but apparently they are in the side case because there is no valve body or anything inside the bottom pan where the filter is.
My question - is there some type of throttle signal that controls the shift points? The older 350/400700 trans had a throttle cable that increased pressure inside the valve body to control shift points under acceleration. Since the throttle is electronic on this car (no throttle cables) there must be a throttle signal and controller of some sort that controls the shift point under various acceleration conditions. Is there any way to check this out? I do have a scan tool that reads live data. I would like to do some testing before I tear into the transmission and start replacing shift solenoids.
I have only driven the car a few miles since the filter change and tried using light and heavy acceleration. The lag is there no matter how much throttle you give it.

Is this problem new? How long have you owned this car?
Could just need programming.

What carfixer007 said ^^^^^^^

. . . and:

What is the fluid level reading on the dip stick?

This comes from the PCM.

I beg to differ. The 350 and 400 worked off of a vacuum modulator. The 700 had a throttle valve cable though. Your transmission has neither, although it used to have a modulator back in 1997 and earlier. The PCM controls it.

The electronic throttle pedal tells the PCM where the throttle pedal is, then the PCM takes this as a request that it gives it something to think about, then the PCM tuses this knowledge and its programming to act by telling other parts what to do (including the engine and transaxle.

You need a scan tool that can cause send test commands to the PCM and that can read pressures and sensors in the transmission.

Since it shifts, albeit at the wrong speeds, it'* probably not the solenoids all of a sudden.

Was the transmission full of gunk when you changed the filter?

Just bought it to fix up and re-sell. I haven't driven it much at all but want to address this before I sell it. The only mechanical changes I made is new front hubs and now the filter change. It runs and drives excellent except for the shift lag.

Is there a separate TCM (transmission control module) and if so where is it? The PCM is located in front of the battery and fuse box in the engine compartment but I don't see a separate TCM. The auto parts stores do show a TCM with just one 49 pin connector whereas the PCM has three connectors.

The fluid looked good, no grit or chunks in the pan. I've changed lots of transmission filters and am familiar with what to look for, and this looked normal.

Thanks for the input, I will probably have to find someone with a capable scan tool. I am going to check it with mine, just to see if it is capable of getting any information even though the check engine light is not on I might be able to retrieve some information. I am also going to keep an eye on the TPS input while driving, I will let you know what happens.

Has it ever shifted properly since you've owned it?

I just bought it to fix and resell so have no knowledge of its history

Okay.

Has it ever shifted properly since you've owned it?

Get it scanned by someone with a Tech 2 scanner. You probably have a P01811 code.

I have a scan tool that can read codes, live data, etc. I checked for AT transaxle codes today and all it showed was PO572 and PO573 which refer to voltage at the brake light switch. I also discovered I have no brake lights. The "pedal" fuse on the fuse block located on the right side of the console is good - tested with a test light - but there is no power at the switch. I don't have a wiring diagram for the brake light switch. I can't find any other fuses inside or under the hood that refer to the brakes, should I be looking somewhere else? I don't have an owners manual for this thing.

I don't know if this has anything to do with the transmission but I do know it might be the issue with the cruise control not working. Either way, I need the brake lights to work so does anyone have a wiring schematic. 2006 Chevy Malibu MAXX LT 3.5L, automatic.

Update - I found a wiring schematic on line that appears to be correct, it has the right color wires anyway. It shows a brake pedal position sensor (which I was thinking was a brake pedal switch) with brown wire as Low reference signal; white wire as 5V reference; and yellow wire as pedal position sensor signal, all coming from or going to the Body Control Module. Does this sound correct?
I was looking for power at the brake (switch) sensor using a test light, I will retest it for the 5V reference with my voltmeter. According to the schematic there are a 1K and 3K resistors inside the sensor so I should be able to test the sensor with an ohm meter across the terminals also. Since my scan tool found codes of both high and low reference voltage detected (PO572 and PO573) I am thinking the switch is bad.
Will let you know what I find out. After that'* fixed, I will get back to checking the transmission shift issue.