99 grand cherokee, 100K, never beaten or off raded. Has automatic transmission and 4.0L.

When accelerating shifts fine from 1st to second, however around 20-40 mph it gets hung up and won't "downshift" into 3rd. It eventaually does but it definately does not sound right when the engine is "revving" up around 2000 rpm before downshifting and comes back to 1200 RPM or so.

It seems to do this more often on cold mornings. I serviced the tranny (fluid & filter) probably 20K mi ago.

A previous thread mentioned using crysler ATF +4 to remedy chreokee shifting porblems...could this be it?

Any ideas?

they shift hard when cold anyway, but the +4 upgrade helps a lot with this.