W.S.
If you aren't facing any issues with 0w-20, I would suggest to continue using it.
Hmmm... Regarding gear oil for Prius, I think, 140,000 Kms is a very high no. It may be changed at max. 60-80K Kms. Regarding coolant, yes you may change it right now (i.e. you may change both coolant and gear oil).