Are you squeezing the hell out of your glutes as part of your set up for each rep? If so, stop. Don't do that. Just the quads and the trunk. The quads squeezed to the point where they feel like they're going to cramp. And the trunk with emphasis on the anterior.
Bring your grip in at least a finger width and "float" the bar in the rack position. Bring your wrists forward so the middle knuckle of the fingers are pointing to the ceiling and get your elbows up. With the correct grip and elbows up, you should be able to support the bar properly without having to start in a slightly leaned back position.