What are you doing for skill training and honing?
Do you play just the rounds or are you taking time to train certain motor patterns to ensure that when you apply them during the round they are already "cemented"?
Obviously it would be important to have a visual evaluation of your swing, but my mind quickly goes to you basically overthinking your swing. If you begin to overreach your concentration levels you will run into issues of trying to muscle the ball down . In cases like the big hitters obviously they put a lot of "body" behind the ball, but they have trained that motor pattern specifically for it and tailored their swing for it. Guys who consistently look to hit the ball FAR versus hitting the ball WELL(which translates into better contact and more distance) always end up trying to put every little muscle behind it. In cases like that, your shoulders drop to try to power through and you get under the ball, or your forearms stiffen up and your shot isn’t as “handsy” as it should be – which would equate to shanking the daylights out of the ball.
I would be willing to bet the “groove” you mentioned is probably a time where you are playing but you aren’t really thinking “I HAVE TO HIT LONG” – I would bet its something where you play to enjoy the day, or you get wrapped up in the good time you're having with your partners, your weight transfers perfectly, your shoulders stay nice and level which in turn keeps your club level, your hands turn over perfectly.
I would recommend going to the range, and starting with your 5 wood, which is obviously easier to control hit some balls. Completely free your mind to the point where you stop caring about how far you are hitting, after you get consistent, whatever the distance, move to your 3 wood, and hit some more - keeping the same mindset. Who cares about hitting long, focus(without overthinking) about a nice calm fluid swing with little to no effort on the downswing. If you can consistently hit 10 balls, then move to your driver. Take those same patterns that same thought. Stop worrying about the distance, focus on a swing that is so effortless that you expend so little energy that you could hit 1000 balls.
I have a strong feeling you are overthinking and getting to the point where you think "Gotta hit long" on everything.
250-275 is a SOLID drive - 300 is great, but not every single person can consistently hit it and be able to play round after round of golf - which tells us theres a big "effort" involved in it.