I think a good workout if you want to improve that is the GCN show "random HIIT" workouts. Instead of spinning at 100+ rpm for the random "hiit" in their videos........stand to climb instead. It's like 2min at SS then a 15 second "hiit" for a total of like 8min per set. Like 3 to 4 sets.
It's exactly the scenario you'd run into. Steady riding at some level of difficulty with a few short harder efforts in there. Just choose to climb out of saddle for the harder effort instead of spinning fast like they say in the video.
I do the SS at like 85-90% power and the hiit's at 140%+.
Here: