98 ES300. 125K. The vehicle has developed an intermittent hard shift between first and second gear. You only feel it under lighter acceleration. If you accelerate faster you will not feel it. Fluid looked fine and had it changed with no improvement. Seems more noticeable going around corners but I think that is because the car is going slower with lighter acceleration. Does not feel like there is any slipping, The shift between all other gears is fine. My thoughts run to transmission, motor mount or possible drive shaft. Any help would be appreciated.

Thanks, Tom

 

Not sure if this could be it, but check the torque strut. It is the "dog bone" upper engine mount.
On our 2002, you could not tell it was broken as it had rubber dust shields on the ends, which hid the broken inner rubber isolator/bushing. The 2002 and 2003 MY have a hard 2-1 downshift from the computer; the broken mount made ours much worse. Cheap mounts are available from RockAuto or Ebay vs. NAPA or dealer prices (huge difference). Not an identical problem as yours, but I could see it as a possible cause.

 

+1 on the dogbone mount, the clunk on my 01 was only during downshifting from 4-3 and 2-1, but that solved my problem too