My car suffered from the infamous clutch buzz, so I brought it in and they installed what they called an upgraded clutch kit. Things seemed fine for about 2k miles but now after the car is warmed up I get serious clutch shudder, especially just after the car settles into idle, the shifter shakes and I get that 2 seconds of rattle. Also happens if I lug the engine even in the slightest. Shouldn't the clutch upgrade have fixed that problem?

 

I can't tell from your description exactly what it is you are doing to make this happen. My only comment would be that if you lug this engine to any extent, it will shutter and rattle as a normal course of events. This has little to do with your clutch.
Please give a more detailed description of what you do to make this occur if I've made the wrong assumption.

 

xviper: R U saying that it will shudder from the lugging, or perhaps that the motor mounts get damaged?

It sounds off the top that the install did not go quite according to plan - did they perhaps "hot spot" the clutch during their road test? There is a procedure on the NSX to bed in the clutch when new, and mine was damaged when the nitwits unloaded it from the carrier truck! After 1 day, I took the car back, and I was soon on the phone to the engineers in Cali since the techs knew I knew more about the NSX than they did. I got a friendly engineer who diagnosed it as "judder" - a combination of the flex from the Targa top, and the hotspotted clutch. The dealership replaced the clutch, and then I personally bedded in the clutch with the Service Manager as co-pilot. Several slightly slippy engagements, with a cool down of about 1/8 mile between, and the job was done. If the mechanics took it for a test drive, and were not skillful as stick men, they could have messed it up, although your symptoms sound like the install is also suspect.

 

I was primarily refering to "lugging". It's really hard to tell from Sparta's post exactly what he's doing.

I key in on these statements:
"especially just after the car settles into idle"
and ....
"Also happens if I lug the engine even in the slightest."
and ....
"the shifter shakes and I get that 2 seconds of rattle"

These makes me think he's "clutching" at extremely low rpms. When I'm a bit "sleepy" or lazy, I can duplicate his symtoms. Let out the clutch at near idle, not give it much gas and the car will shutter and rattle till it can get enough road speed and throttle for the available torque to move the weight of the car.