Every morning for 6 months we would need to "unstick" the gas pedal by pushing it harder than normal to get going. After that it would drive fine.

The other day it was very stuck and I needed to stomp it out. I started driving and the car was stuck in first gear. I found under the hood the lower transmission cable was snagged under a bolt head on the engine, not allowing the transmission to know when to shift. I unhooked it and drove it to get fixed.

I guess when you have a sticky gas pedal, either the upper throttle cable or the lower transmission cable needs to be replaced. We had been lubing the cables for a while but it doesn't last forever. It cost $360 to replace at a Volvo dealership service center. Hope this helps someone in the future.