Whoa whoa whoa... What? I've been trying to figure out that stupid stuttering for years, I just thought I had put too much wear on my transmission or something. You're thinking it could be a bad o2 sensor? If your problem is the same that I'm having and the o2 sensor fixes it, well I'll be damned. Thanks.
I put Sachs shocks on there. Here's what I bought from ******************.com:
Shock Absorber and Strut Assembly Sachs Shock Absorber and Strut Assembly X3|2.5i Sachs
Price: $ 135.95 Qty: 2.00 Part #: W0133-1805976
Shock and Strut Mount Lemfoerder Shock and Strut Mount X3|2.5i Lemfoerder
Price: $ 24.95 Qty: 2.00 Part #: W0133-1806541
These were for the sports package suspension, not sure if they'd be the same for you.
I had my front ones replaced at a shop, kind of wish I had done it myself. BUT it was totally worth it! I did it at around 99k.
So back to the stuttering... I feel it most when I'm in a middle gear, maybe 3rd, going up over an underpass on the freeway, and is worse when someone is riding in the car with me. Is this similar to what you're experiencing?