[12 piece bucket]

First place I'd look is plane. If you can't straighten the right arm down and OUT, you are probably over plane through impact.

Split grip drills, no ball, just in the air, below horizontal, but not lowered all the way to a full swing.

Focus on first - not letting the clubhead get 'inside' the hands until hip high, and second, swinging OUT - from about 7 to 2 on a clock as your right arm straightens to 2 o'clock.

If that doesn't help you get a good feel for how the right arm needs the 'room' to straighten, next look to your pivot. You may not be turning through very well.

.

Right . . . right shoulder farther downplane . . . more right arm.