transmission stuck in higher rpm & sluggish to acceleration

Transmission gets stuck in a fixed higher rpm when you release the gas pedal, and become sluggish to acceleration. It appears to be worst on colder days (Temperatures lower than 0 Celsius). It has happened four times in the last 3 weeks.

Subaru must know that parts of Canada are cold during the winter months? When I start the car on a cold 5 F (-20C) morning, it accelerates very slowly, requiring a full throttle to merge with traffic. One time, I experienced heavy vibration from the engine/transmission when accelerating from cold start. I could not back off because I was on a 60mph road with traffic bearing down on me. Hope there was no damage. It has since cleared up.