my girlfriends sister has an 02 accord sedan 4cyc auto with about 90k and she has been claiming that while on the highway doing about 70mph the car start to slow down and wont upshift. i have checked the trans on the car changed the filter, oil you name it and every time i drive it no problems. i know is cant be a vaccum line or kickdown switch like in older cars but the car shifts smoothly so im not sure if its the tranny. I havent felt the problem only heard of how the car acts, im thinking maybe it the motor being pushed too hard she likes to drive it like is a big block 454 in it. can anyone help diagnose this problem?

 

First, take it somewhere and check for any stored or pending codes.

Tune up items are up to date?

 

No i asked her about it yesterday and she has never had a tune up, air fliter change, fuild changes execpt oil and brakes. idk why people own cars.