You seem like the type that would really enjoy training to power. It sounds like you don't have one on your current bike (pardon if I missed it in your post), but training to power has opened my eyes to training. You can find used Stages L-sided power meters for $300~ pretty easily nowadays, and it will allow you to fixate on a power target rather than a personal best which is more sustainable and repeatable (and will allow you to hit your goals more often). So, instead of attacking a hill to try and beat your previous best time, you can effectively do repeats at a set power and pace yourself accordingly.

Check out the TrainerRoad podcast for tips on training... their viewpoint is that most riders need to ride harder during the hard days and easier during easier days to see the best process. I fell right within that bracket... I would accumulate decent training stress each week but was not making the adaptations and progress I wanted. Now that I train to power, and I know what 3-minute VO2 Max intervals feel like, I realize I wasn't even really training before.