Transmission problem(s)

About a month ago I was driving on the freeway and lost 5th and 6th gear. Put in neutral and back in drive and got them back. Check engine light came on and error code was showing the need to replace the solenoid. I took it to a shop they ran service which was taking the fluid out and adding new fluid. Told me to drive it for a month and see if I have issues. Since driving the 4th gear makes whinning sound never fails. Only when switching to 4th. I called the shop but mechanic is out till next week. Anyone know if this means I need a new transmission?

2019 Yukon XL 108k miles