I'm surprised you find a lack in body with an IPA that starts at 1.073 and ends at 1.020. My go to IPA grain bill is 90% 2-row, 6% c20, 2% dextrin malt, and 2% simple sugars (cane, corn, brown, raw, whatever is available in the pantry), and it finishes at a perfect 1.010-1.014 (og dependent) for my tastes. That said, what you have doesn't look bad for your goals.
Other than the gypsum, what else are you doing about your water?
Your hops can use some adjustment IMO. Citra, while I am not a fan, is wasted at 60, and I like to blend more for the later additions. I too am a fan of the 20 minute addition, but I exclusively use Columbus there. Throw some mosaic, simcoe, Galaxy, centennial, or any other west coast hop in with the cascade to give a more layered hop profile towards the end. I almost always have at least a smidgen of Columbus at 0 at dry for that dank hop flavor.