I would suggest some split grip drill practice for you. You are very likely rolling/lifting in the takeaway and getting off plane.
a few things to keep in mind with split grip drills (one of the best drills you can ever do IMO)
1) the butt end of the club should move at the same rate as the clubhead in the early takeaway (the reason TGM uses the bent left/flat right at address, keeps you from coming 'out and over' right off the ball), feel like the back of your lead hand faces the ball a bit longer going back
2) the butt end of the club should move 'nearly' straight back, until hip high where everything 'meets' in line, on plane
3) as you do the split grip drills, exaggerate the 'throw' of the right hand 'out to first base' - this will give the 'push' feeling and the 'uppercut punch' (but don't forget full roll)
The throw of the right hand can be thought of as an 'upside down' fastball, I find people understand that feel a bit more than the 'underhand throw', which implies more of a toss motion, instead of a 'throw' motion
Or, as Tiger mentions in his book - try to get the butt end of the club as far from the right hip as you can on the backswing
It is similar to a hockey motion from hip high through to the finish - feel the right arm extension 'through'
Practice from hip high on the back swing, to a full balanced finish
The right arm extending, from the 'inside' is a critical feeling to get, and you can't get there if your takeaway is off, as most folks are, the lift/roll (not keeping the clubhead 'outside' the hands until hip high) will ruin any chance of proper extention, so work those split grip drills until it clicks for you.