hello. i have a 1999 2.3 CL with an auto trans with 142k on it. to my knowledge it is the original trans. i bought the car 3 months ago and i am the 3rd owner. i know the trans has been flushed once and maybe twice at a lube place because i saw the records.

my concern is when the car is cold (the first 10 to 15 mins of driving) the trans will spike the rpms about 500 rpm and then shift hard into the next gear. this is only for upshifting. once the car is properly warmed at about 15 to 20 mins the shifting becomes much smoother.

i have used auto-rx before and spoken with someone who used it in their TL trans with great results. i am going to give it a shot and then i planned on flushing the trans after wards but i am actually reading on here to just drain and fill the trans. that seems silly. a flush is simply running the car while on the machine and letting the old fluid catch in a basin while the machine channels new fluid in.
questions:
why would that be dangerous?

why is the trans behaving as i described above?