[cardoc]

A couple things that stick out here: Shudder and hard to start. The "knocking" is still up in the air.

If you have access to a scan tool that would allow you to look at live data, you may want to check the output of the front AF sensor. It could be running rich on fuel which would cause a shudder on acceleration. The hard to start issue seems like a sticky IAC valve. Clean it and see what happens. Could also be a poor signal from the ECT, engine coolant temperature. If it is sending the wrong temperature to the ECM it can be difficult to start.

Start with the engine performance first and then see how the transmission reacts. All the transmission controls rely on engine data to function.

The drifting, good call. Two things that cause drifting is tire pressure or loose suspension/steering.

 

[cardoc]

TPS hardly fails but it could create issues with the acceleration and transmission.

If the engine runs rich on fuel, it will lose power. Same with too lean. You just need to see what the computer sees to determine what's going on. So far, you're on the right track. At least your not blindly throwing parts at it.

 

[cardoc]

Did the rear O2 waveform or voltage alter rich/lean as in he video on my post in P0420 Diag; post #13? http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diag-2.html

As with any bearing, it's design is to allow rotation of the suspended part(s). The carrier bearing doesn't hold much weight but can wear, generally the isolation bushing will rot, often the bearing dries out. There should be no movement in the assembly.

Just a shot in the dark, but have you checked the rear brakes? Parking shoes? If its not in the transmission it may be a mechanical issue with the rear brakes causing extra load on the drivetrain when torque is applied. I had this ONCE a few years ago where the brake was holding on a wheel due to a bad seal in a caliper. Subsequently causing a vibration and occasional popping noise. Rebuilt the caliper and the issue was resolved.