I don't mean to imply anything about you, just want to say this so please don't take any offense, but many times people don't notice things about the cars for some time, and once you notice it, the "problem" sticks out for some time.. For instance, the first time I do pretty much any repair I am extremely cautious with it for a good 5-10k to make sure I don't ruin the car. After the first time I flushed my tranny I think I checked the fluid every couple of days because I was worried I did something wrong..

Anyway, what I'm getting at is that I think it might be possible you haven't really used L much and notice how quick it decelerates you, as well as the shift-lock. If I read your post right, you noticed the lock-up and that it reacts different in L than it does in 3 and D. When you played around with the shifter the PNP code was set (which takes some time shifting between 3 and L to get it to set). I wouldn't worry too much about the code since it hasn't reappeared and really only showed up when you screwed with it. Anyway, I think due to one of the planets freewheeling vs locked results in the different experience. Mine does it too. If you were nearby I'd want you to drive mine and see what you thought, however you in CA and I'm not. Perhaps you could test drive another 850 and how similar they react (check a craigslist post and see what you find). Sorry about the rambling..

I think you're most worried about the tranny but I wouldn't be. It seems to me that its reacting as it should.
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If you're not driving it "like its stolen," are you really driving?