you nailed it, i have the book inner tennis, same author as inner game of tennis. and he says the exact same thing, you are lose and let your inner natural game take control when its out and ti doesn't matter and so when you "try" to hit a long serve, you swing away and your body unconcsciously does all the movement and everything. the "try" is in quotes because that's exactly what gallway says we do on normal shots and normal returns, so our conscious thinking self does the whole "ok watch the ball.. stand a foot ahead, bend your elbow, bend your knees.. no the grip's supposed to be this way" and then when you hit it long or something, everytime since then it goes "you moron, if its a kick serve you step in, step in.. and don't mess this one up.. keep your legs bent and swing through" and such, and that's what "try" often means and you are not letting your inner game through - like you do on an out serve return.
he mentions this exact scenario too.