During mild acceleration it will shift into 5th too early and shudder. If I step on it a little more it will downshift back to 4th. Under hard acceleration it's fine, or if I use the paddle shifters.
Would it be the 4th gear shift solenoid or the 5th gear solenoid?

 

Its a 2011 TL SH-AWD with the 3.7.

 

My '13 does the same thing. It's designed to upshift as soon as reasonable for fuel economy. Yes, if at 40-45mph or so it's in 5th, and if you need only light acceleration it will shudder a bit. I had the dealer check it out a year or so after I bought it (CPO, 6 years ago) and they said it was normal. To me it just doesn't downshift quickly enough with light pedal pressure, but as you say more of a push, or paddle shifting, solves the problem. Since I was told it was normal I use the paddles. The 5sp in my 07 TL was more responsive to my right foot for downshifting than this transmission.

 

Thanks for the confirmation. I might think this is completely normal if it was not for the fact that in didn't use to do this. I suppose I will have to just live with it.

 

how old is the trans fluid? Have you done a 3x3 fluid change?

 

The car has 52k miles. When it was in for the airbag recall I asked them about this and they changed the fluid but it made no difference.