I am having a problem with the Transmission shifting. The transmission is not at fault. The Mechanic seems to think the problem is electrical originating from the PCM module. Any answers?

Here are some possible causes and steps to consider:

Check the transmission fluid level and condition. Shifting issues might be caused by low or filthy transmission fluid. Check that the transmission fluid is at the proper level and seems clean and red. If it is low or polluted, a fluid change and filter replacement may be required.

Transmission Solenoids: Modern automatic transmissions employ solenoids to manage gear shifting. A faulty solenoid might cause the transmission to stay in one gear. If needed, a professional can diagnose and replace malfunctioning solenoids.

Transmission Control Module (TCM): The TCM is in charge of controlling the operation of the transmission. It can cause shifting problems if it malfunctions or receives inaccurate sensor data. Check the TCM for fault codes and functionality.

Wiring and Electrical Issues: Examine the transmission's wiring and electrical connections, especially those to the TCM and sensors. Damaged wires, faulty couplings, or electrical issues can all disrupt transmission operation.
Shifting problems can also be caused by internal mechanical faults within the transmission, such as worn clutches, damaged gears, or a malfunctioning valve body. These problems can be diagnosed and repaired by a competent transmission mechanic.

Transmission Fluid Pressure: Proper gear engagement is dependent on transmission fluid pressure. Shifting might be affected by a malfunction with the transmission pump or pressure regulator. A pressure test can aid in the diagnosis of these problems.

Examine your vehicle for Diagnostic Trouble Codes (DTCs): Even if the knock sensor problem has been rectified, there may be more DTCs associated with the transmission problem. Check for any stored trouble codes with a diagnostic scanner to gain more insight into the problem.

I hope this might be helpful.

no info generic answer have vehicle scanned for trouble code[s]

there are a number of shift solenoids in a transmission so unless the mechanic was specific as to what ratio is involved , it will be a case of replacing the wrong one
A lot of the time ,harsh shifting is from dirty oil and or oil pressure problems
May be it would be best if you went to an auto transmission specialist shop for a fault code reading and a proper diagnosis

Hello
1st let me explain how the transmission in this car is shifted, there is a computer control module, it is called the "Powertrain Control Module" or PCM, some cars have a separate computer that is just for the transmission, this is a TCM, your cars PCM does both jobs of running the engine and shifting the transmission. The actual shifting is done by electric solenoids inside the transmission which the PCM controls by grounding them, when the computer determines it is time to shift based on vehicle speed and transmission fluid temperature and other inputs from the engine sensors it grounds the proper solenoid that shifts the transmission up or down to the appropriate gear, it monitores the shift electronically and if it doesn't see that the transmission has done what it was commanded to do it sets a fault code in its memory. I have read your problem and no mention is made that "Your Mechanic" scanned the system for fault codes, if he did and nothing shows up then you have a mechanical fault in the transmission and it will need to be torn down and rebuilt to correct this shift problem.
My experience is 25 years as a Ford factory trained repair and diagnosis technican.

try web resourceful.com for auto manuals online

Depending on where you connected power to the stereo from on the fuseblock you could be messing up the tranny. Refer to the manual versus where the stereo wires are, Worst case, disconnect power to the stereo to see if that's the cause of the problem.

This problem could only be diagnosed is by downloading he fault codes from the transmission control module (TCM) you need to go to your Subaru dealer. I have access to the codes, but you need to know what codes are grenerated by your transmission.

The shift solenoid is located under the side pan of the transmission. It's not a easy job to take the side pan off. May cost $700 for part and labor(both including).

Those codes are tied into the transmission and odds are your transmission is not shift properly because it's detected a fault.

P0751- the solenoid should be located under the side cover assembly on the driver's side of the transmission. You may have a short in one of the wires and or a bad connection with the harness. This is probably going to run around $500 and up.

Your right in as much as it shouldnt need complete over haul but a competent auto trans technician to clear the shift fault.It could be a solenoid or check valve that should be able to be repaired with out the transmission having to be removed.