I've had this Sienna since 2020 Bought with 50k miles, now has 188k miles, we do a drain/refill every 30k-50k miles on transmission (We've watched your videos on this and do exactly as you say, replace exactly what comes out))
I drive a lot of highway miles so it still purrs like a kitten (and we change oil every 5k with Mobil 1 and lucas) 
We do all maintenance on it (CV Axles were changed at 75k (surprised they only lasted 75k? But this new set has lasted over 100k so we are doing good). I keep good tires on it at all times (just bought this set in December)

The problem: When I start the van up and put it in reverse, it kicks a little but when I put it in drive, its more noticeable? Its almost like my foot isnt on the brake hard enough? (But it is) We changed all 4 motor mounts today (2 were pretty worn *dog bone and front) the side ones were ok (but we changed anyway) I really figured this would clear up the problem but apparently not. CV Axles are fine. What else could make it do this? I know the 2017 has the new transmission that year. Could it be the higher torque in first gear is doing that? Or maybe control arms? I'm not having any issues with shaking while driving, no clunks when turning etc. I know a lot of people complain about the shifting on these and there might be an update i can get on the software? Thing is I dont have time to be without my van too long so dont want it sitting at Toyota for too long if that's not the problem. So I would like to rule out other things if it could be the issue. Its been doing it for a long while. Transmission works fine, no issues at all.