So I've held off from posting this as I really wanted to exhaust my local resources for resolving a new issue before posting.
I recently had some 90K maintenance items done and a new issue has arisen (perhaps coincidence but anything is possible). New plugs, LWCP, accessory belts, trans/diff service and oil change were completed. My clutch needs babying as it's been slipping a bit under WOT so I went a couple days before needing a quick WOT pull to pass someone.
Now consistently, when in 2nd or 3rd gear, at WOT only, my car feels like I hit the rev limiter at 5K RPM. Every time - without fail. 25%, 50% or 75% throttle it will accelerate as expected, and doesn't cut out all the way to redline. When I hit that wall, I can lift and get back on throttle and the car drives smooth. Car is Stage 2 and drives exactly as expected except this one situation.
I talked with my tuner for input, as well as my local Subaru mechanic. Tuner had me log and it looks like I'm lifting off when the cut occurs (although I'm not). No CELs or codes whatsoever. I talked with my mechanic and he thought for sure it was the fuel pump. I wasn't sold this was the case, but since I planned on getting one down the road, figured I'd go with his experience and pulled the trigger on a DW 65C. Installed and the symptoms are exactly the same prior to the new pump.
I am open to input. I've cleaned the MAF, reset the ECU, installed a new fuel pump, logged FPDC and IDC and no smoking gun yet. Only occurs under full load at WOT. At this point the mechanic says it's the tune (finger pointing in my opinion), especially since my tune's been flawless for over 4K miles.
I truly doubt a tune would do this in general - especially after so many non problematic miles (and my analytical side says if you just had work done, and a new problem arises - must be related). My mechanic has been working on Subarus for many years and is pretty sharp and quite capable, but I think the tuning aspect of things is beyond him, so an easy place to shift the focus.
One other issue I have had occur a few times that seems like it's plausible it could be related is that occasionally when I'd be rolling into a stop, and clutch engaged, my car would rev a couple thousand RPM on it's own with zero throttle input , (even before I was tuned to stage 1 let alone stage 2). I'm wondering if it's related and maybe something with a throttle sensor, the DBW system in general, or is my car just possessed by throttle gremlins?
Open to input, things to try, or discussions that might flush out what the hell has started to act up in a normally healthy car.