Another update.
Did a band adjustment. Reset the ECU by removing the battery for awhile. No codes are presently being set. Went back to the tranny shop that did my rebuild and they gave it another road test. Said there is no slipping in the transmission. Ran a stall speed test and gave me a file they pulled from the net somewhere (I'll attach it below - said it was on Subaru's but not the SVX specifically). Since the stall speed was if anything slightly low in D, 2, & R, they infer that the road test is correct, no slipping of bands, etc. I asked again about a slipping stator and they said no, as I would be experiencing poor off the line performance, and in all gears, not just trouble in the higher gears.
They said they would do a line pressure test (for around $100), but thought I would be wasting my money. I think they think I'm a bit daft over this transmission (maybe I am, but I don't think so, transmission behavior is definitely different in the last few weeks from the 20 months preceding).
So, as I see it, I could get a gauge and do a pressure test myself - but don't know how. Will a pressure test reveal if the solenoid pack is going bad? I'm about out of ideas. EDIT: I previously reported that the slip went away during the time I had TC lock-up. That seems no longer to be true, if it ever was. From this I infer the band is slipping. But since it passes the stall test, I'm now guessing I have a problem with the A solenoid. END EDIT
So, at this point I see two likely alternatives: a) solenoids failing gracefully (can they do that?), or b) lee is an idiot. Safe money would probably be on choice b.
