I'm happy to report that the Fremont Service Center successfully upgraded my Signature P85 with the Performance Plus suspension and I picked up the car today. I'm totally amazed at the transformation in the handling. All of my previous complaints about "floaty" freeway lane changes, understeer on freeway on-ramps, pitching and bucking on hard acceleration/deceleration, etc. are gone. They are replaced with a car that goes where you point it, is extremely predictable and forgiving and has more grip than you think is possible in a 4600 lb. large sedan. The sacrifice in ride quality is minimal - the only place I notice it is when driving on uneven pavement or over freeway lane divider dots.
I've been petitioning Tesla for at least 4 months to get this upgrade. They have been hampered by very limited availability of the P+ suspension parts. They are starting to do a few "learning" retrofits as the parts begin to be available, and I was fortunate that they picked me for one of the very limited slots. I chose to get a full upgrade (same parts as in a new P+) for two reasons:
1) The early VINs require the subframe bushings to be replaced, so I was already needing much of the labor required to do a full upgrade
2) Tesla does not have any partial retrofit (bushings and wheels/tires only, no swaybar or damper upgrades) cars available for test drives. So I was unsure if I would be happy with the partial retrofit, but I knew after 2 test drives that I would be delighted with the full P+
Tesla has asked me to not disclose the cost of the upgrade because it is not yet an announced product. They do plan to make P+ upgrades generally available as soon as they can. What I can say is that I am very happy, and the cost of the upgrade was definitely less than it would have cost me to sell my Signature P85 and buy a new P85+.
Last point. With my 2006 BMW M5, I used to routinely take my favorite freeway off ramp at 45 mph, with a personal best of 47mph. In my first attempt with the P+, I nailed it at 45 mph with no tire squeal or sliding, so I know there is more speed to be had. I can safely say that the P+ handles as well or better than a BMW M5. :biggrin: