High rev on shift into top gear

All,

Once in a while my Fiance complains that her 2000 P11 auto trans revs up really high on the highway and then seems ok.

It sounds like it is either slipping or not shifting cleanly into the last gear.

It seems to happen more when the car is cold.

Any ideas?

Thanks,

Rich

Sounds like the high clutch{inside trans} or the torque convertor clutch.Either way any rpm flare-up is usually an internal trans matter.
Sorry