Service Engine On... Transmission?? MAF??

Car ocassionally shifts really hard. Not all the time. And the service engine light is on. Noticed today that also a whine is coming from under the hood and it is not shifting into overdrive. Shut the car off and restart it, and it shifts fine,still no overdrive, no whine, but the light is on. Drive about 15 miles and it will shift hard again.
Stopped by Auto Zone to have it scanned. Code came up P102... Mass air flow sensor. He could not read tranny codes. The MAF sensor may be bad, but I can't believe that would cause the shifting problems. After looking on this forum, it sounds like the PCM sticking in the tranny. Car is a 2000 GT with 120k on it.
Any help would be appreciated.

I added some seafoam from NAPA and it helped for awhile, but it still does it.

The MAF sensor could cause erratic shifting but it sounds more like you have other internal problems with the tranny. Possible PCS or 3-4 shift solenoid at the valve body. To scan for tranny error codes you need an odb-ii scanner that is trans. capable. Also, since you are missing OD (4th) you could have a mechanical problem like the 4th clutch or a spline.

On the MAF sensor error I would reset the PCM and see if it repeats. But P0102 is typically a bad MAF sensor.

I agree with bnaylor 100%

I agree with bnaylor 100%

I'm with you fellers.

Looks like I'll take it to a transmission shop and get them to scan it. I know that tranny work can be some major $$$.
But I've already got alot of other repairs done already, so it's a question of do I sink more $$$ into it or cut my losses. Other things needed are the fuel pump sensor since the gas guage doesn't work, the struts should be replaced, as well as new tires and brakes.
Just replaced 3 hubs (thanks Rich), ignition switch because it would not come out of park, 2 window motors.
Thanks for the replies...

I guess it depends on if the car is in good shape and if you like it. 2K for a tranny is lot cheaper than a newer car which could give you the same problems. If you don’t want to car try and sell it as is or find a junk yard tranny and trade it off. Me personally if the car was in good shape I would fix it regardless if I liked it or not. The I'm bored of it or I don’t like it anymore so lets get a new on lead a lot of people into bad financial decisions. You have to look at the cost to fix vs. the valve of the car.