My 2000 S80 T6 still has a little shudder in the tranny from 2-3 and 3-4 even after I flushed the fluid myself and replaced with Mobil 1 synthetic. I used the directions found on this site. Has anybody tried the lubeguard tranny treatments to eliminate tranny shudder.

I run a repair shop Lubegard products work great
DID YOU CHANGE THE FILTER
remember this is a GM transmission (4T65E) you can buy a filter at the local parts house for cheap $10.00 or less (reuse the pan gasket)
you allso should check out GM SERVICE BULLETIN 00-07-30-002B

How long did you wait before posting this message? Sometimes it can take up to 500 miles for the new fluid to do what it needs to do to eliminate/reduce the shudder. I'd give it some time and monitor fluid color.

Only 200 miles. Although frank said this may be covered under my Volvo Certified Extended Waranty. I'll wait a bit longer and then take it in.

There are dealer only TSBs from Volvo on the subject so before trying more chemicals, try a trip to your dealer.
Could be software and/or an STH solenoid mounted to the valve body (a 7 hour job) that might cure your problem.
As for synthetics or flushing, that never cures a problem that already exists but being that you flushed the trans, (if higher mileage) did you replace the GM trans filter above the pan too (not that I think that's causing your problem but....)?

Frank what is a TSB and how expensive is this software and solenoid fix? Did not drop pan and change filter. Has extended waranty. Currently 62000 miles is this covered

If VIP (assuming?), they don't cover software but it costs about $25 and it's about 1/2 hour labor, warranty time.
VIP DOES cover the STH solenoid and even a replacement trans if need be so that'd be the cost of your deductable ($55).
I'd advise taking the car to your dealer BUT don't tell them about the synthetic fluid as they might not like that.

I have a '99 S-80 that had a "shutter" (you can see an earlier reply), the transmission was replaced under ext. warnt. at 80M miles. Now at 115m, the shuttter is back. Does that mean that it will require a new transmission ?

-Doug