I had this problem with the tranny in my 2000 Silo.
When you get the 'slamming into gear' (otherwise known as a 'harsh shift') action, The problem (in my case) was a worn low pressure solenoid (inside the tranny).
Now, because your tranny was flushed, I suspect this solenoid has sucked in loose foreign matter and may be plugged now.
Did you have the tranny fluid drained and screen cleaned before the 160k rolled around?
The mileage recommended is around 60k unless towing a trailer constantly or any other 'severe' condition.
My tranny shop tech recommends changing the fluid (NO flush) every 30 to 40k miles when the vehicle is used under 'severe conditions' (towing, constant stop and go, etc).
You MAY get lucky with another fluid drain , but that's a big maybe.