definitely would chalk up the gasping to being on the trainer in the garage. I tried a trainer in a porte-cochere in Memphis and was near death, LOL. Can you go compare to a ride outdoors and see if that changes it?
Motivation is huge; without it, medium workouts seem impossible. We need purpose. Try to reframe the workouts as not only for races, but for your development over time. Things we do this season have rewards years down the line if we’re consistent. maybe a mindset shift would help!
good luck!