Get a more stable boat if you want to do harder runs. Creekboats are great. Improve the brace, and work on a faster roll. Get a consistent 2 second roll.
At the NF Championships last weekend, I saw 3 pros upsidedown in one of the gnarliest rapids on the planet. They almost all hit their first roll in 1 to 2 seconds. Look at how fast this roll is, at 29 sec:
Get a good fullface helmet (like the WRSI) and elbow pads. I've been wearing pogies for knuckle protection on our low water runs. I've seen some seriously bloody knuckles this season from being upside down on low water runs (like you would get from punching rocks with your fists). Take care of those hands.
You can also look into changing the mental/emotional patterns that are leading you to make choices that are getting you hurt, multiple times. Visualize safe lines. PM me if you want more info.