I agree, it was the same for me.

It really took me some form work to be able to run slowly. (The form work also helped me run faster - it's just more efficient.)

Running will also always be more demanding aerobically than cycling, since it's weightbearing.

You'll be happy when it pays off on the bike and you're breathing through your nose while riding up hills that you used to have to stick out your tongue to get air.