Are they all tightened equally?
I just changed my kossel XL belts from no-name to genuine gates 2gt powergrip. No real change in calibration or performance.
Some people have suggested with long belt runs, as found on large deltas, using 6mm gt2 belts that if steps/mm should 80 then use 80.5 as the pitch is only correct for a taught belt and we often don't tighten them enough. Maybe you need 79.5 (or whatever proportion of your default steps/mm).
Might be worth just printing 2 towers one twice the height of the other. Check the z height after printing and if one tower is proportionally larger than the other (rather then both being the same amount too high/low) then adjust your steps/mm on all 3 towers equally and calibrate again.