S60 D5 2007 Transmission problem (Aisin AW TF-80SC 6-speed)

[night_fury]

I bought this car (S60 D5 185 A/T Summum MY2007) which was regularly serviced before and the ATF oil was changed on 140000 km at last service (soon will have 160000 km). The transmission runs through gears smooth and cleans and I really enjoy driving this car. As I sad the car runs sweet as a not until it is out for about 20 minutes and then it stars to flare shift when shifting from 3rd to 4th gear (only upshift). All other gears work perfectly! When the car is cold everything runs perfectly but when it worms up you can fell the flares as I mentioned. I have no messages like "transmission service required" or any kind.

Does anyone have a clue what should I do next?
Anyone had/has similar problems with this automatic transmission (Aisin AW TF-80C 6-speed)?

I was thinking I should go first to a Volvo garage to check the oil level in automatic transmission and to check maybe it only needs a new software upgrade. After that if it doesn't help, maybe I should flush once again the whole system with new (at least!) 10 liters of Mobile ATF 3309. I'm not sure which one they used last time because they offer you Volvo ATF and some cheap alternative (three times cheaper!) but I know that Mobile ATF 3309 is acctualy the original one. If that also doeasn't work then I don't know really what to do... at least for now.

Any suggestions???

I would be more then graeatfull if you guys can help me.

NF

[M-R-P]

Have the codes read and see if anything crops up. The car won't always tell you if somethings up. Other than that, I'm not to up to scratch with autos.