Test driving a 500E with weird shudder

[Holeshot]

So, I love my 300E but I want more power (having had a 420 loaner for a while, I'm now spoiled). So, I found this 500E and took it for a test drive today.

FUN! Power, and it's a W124 (my favorite body by far, but the replacement has grown on me too). Digressing.

When pulling out of parking lots right off idle it would studder, stumble. I could not say for sure if it was massive trans shudder or engine stumble but I'm thinking the trans is really worn out. Too many burnouts? In one thread the ASR was mentioned as having some strange side effects and wondered if it might be freaked out and causing this to happen.

Doing some reading it seems like the tranny is not a special unit and shared with the larger S class 500 cars so I'm thinking if I need to have the trans rebuilt it would not be a 'major' parts hassle. Thus my post.

Those that do this sort of work, what would I expect to pay (drop off car and pickup) for a trans rebuilt barring any unual parts requireing replacement.

About 6 years ago another 300E of mine lost a $100 servo inside the trans but it cost $2500 to have it repaired (trans rebuilt by a small mom-and-pop MBZ shop in Roseville CA).

I'm I insane to negotiate a couple grand off the car for the trans, drop it off at a trans shop and tell them to 'FIX IT'?? Neat car, color I want, interior in good shape and everything else seemd to work well. Could not spot any leaks.

Soliciting some feedback on test-drive diagnosis tricks to narrow down the true problem and some idea of what it would cost to fix if the tranny is going south.

TIA!!