ZanderZ32

iTrader: (2)

The vibration, what I would describe as a shudder, only occurs during heavy load such as taking off from a stop light/sign or in stop and go traffic.
Only occurs in first gear and only between 7-10mph, otherwise the car is perfectly smooth and quiet.
Never had a single issue at any other speed or in any other gear.
The issue hasn't gotten worse since it started a couple months ago either.

Parts Replaced:
Both Front and Rear Driveshaft Couplers with OEM units (Both had some wear)
Driveshaft center support bushing with OEM unit (Had some play)
CV joint inspected and in perfect shape
Trans has fresh Lexus recommend fluid (B&M Oil cooler will be added shortly)

A Lexus specialty mechanic and a transmission shop both ruled out torque converter, but the transmission shop said there is a adjustment procedure for the driveshaft height. Apparently you use shims to offset the driveshaft support allowing it to be straight with no droop.

Any insight would be helpful, I'm out of ideas

Car is a 2004 GS430 with 80k miles.

badblackgs

iTrader: (1)

when ever I'm diagnosing a vibration or shudder during take off its usually front wheel drive cars and its worn out axle shafts. Ours being rear wheel drive might be different feeling but it wouldn't hurt to inspect the axle shafts in the rear. crawl under the car and grab the axles in the middle and wiggle them side to side and see if you notice any excess play.