'99 subaru legacy tranny help

Hey hopefully you guys can help me out.

In September I purchased a 99 subaru legacy 30th anniversary edition with an automatic transmission. It has 186k miles. It just had all the major work done (timing belt, head gaskets, etc...). What I have been noticing lately is while the car is cold and still warming up, if you drive it when it switches from either 1st gear to 2nd or 2nd to 3rd it will rev up fairly high then catch and go. Almost like a slipping clutch in a manual transmission. I am new to subarus and was curious if that's a common problem that anyone else has had? Also if anyone has any ideas as to how to fix it?

Thank you guys so much for the help!