Transmission shift/pressure solenoids

Hi
I have a 2002 Chevy impala. Just a regular impala, no SS, no LS. 3.4L engine. Automatic. Has 115200 miles. MY transmission would work great until about an hour of driving (not over heating) Then it would shift hard. Today the shifting got worst and starts immediately. Today the check engine light came on. I went to autozone and they got a code P0751. That showed up as
1-2 shift solenoid valve performance explanation
Transmission in drive=ECM compared engine speed to probable causes
1.-shift solenoid failure-repair other codes
2,-Internal transmission failures
All the above was printed on a receipt by autozone about the code
I am asking is this inside the transmission? (shift solenoid)
I also read that the pressure control solenoid can cause this problem. Where is this located? Should I try to change the pressure control solenoid first. Where can I find a print out that shows me where these parts are located? I am not a mechanic but can and do minor repairs.
Thanks

Harsh shifting is a common symptom of a Failing PCS, the transmission starts to slip more than it should multiple times, so the transmission maxes out the pressure. But if this is the case there SHOULD be a P1811 code also.

Changing the PCS is far from a minor job. It involes dropping the control arm out of the way, removing the axel, and opening up the transmission.

Heres a Guide :D

http://forums.minnesotamud.com/showthread.php?t=4234

Had the same problem with my wife's 2002 Impala LS. Onstar diagnosed the problem as the Torque Converter Relay over the phone.
HEMI101, perfect help. Your Minnestoamud.com link is perfect and your advice - AWESOME! Thanks!