2007 volvo s60 2.5T AWD harsh shifting up when going downhil

[tmaczz]

Dear All - my 2007 volvo s60 2.5T AWD (54k miles and AT) won't shift up properly when going down slight to moderate downhill sections, especially from 1st to 2nd.
RPM could run up to 2500 before shifting up with a clunk. But it could shift smoothly on flat roads. And I checked the ATF, it was brown.
Does this sound like an easy clue to something that might be wrong?

[vtl]

Change ATF. Mobil 3309, Idemitsu Type-TLS or Valvoline MaxLife, or other ATF spec'ed at JWS3309 or AW1, whatever you prefer.