This is the only TSB I could find applicable to the 2008 Avalon transmission.
TSB 0061-08 . . . . . May 13, 2008 . . . . . Torque Converter Shudder
Section: Automatic Transmission/Transaxle Market: USA
Applicability:
2007 – 2009 Camry Transmission(s): 6AT
2008 Avalon Transmission(s): 6AT
Introduction:
Some customers may be concerned about an intermittent shudder when lightly accelerating after an upshift around the following speeds: 26 mph (42 km/h) (4th), 36 mph (58 km/h) (5th) and/or 44 mph (71 km/h) (6th). Production changes to the torque converter assembly have been implemented to improve this condition. Refer to the repair procedure below for diagnostic instructions to confirm if the torque converter needs to be replaced to address customer concerns.
Production Change Information:
This TSB applies to vehicles produced BEFORE the Production Change Effective VINs shown below.
Avalon 4T1BK36B#8U299716
Camry 4T1BK46K#9U579648
APPLICABLE WARRANTY:
This repair is covered under the Toyota Powertrain Warranty. This warranty is in effect for 60 months or 60,000 miles, whichever occurs first, from the vehicle’s in-service date.
Warranty application is limited to correction of a problem based upon a customer’s specific complaint.