A couple of checks that I would perform are
- in turn remove a float bowl cover on each carb, run the aux pump and measure how much fuel you get out in 5 mins. (do you have sufficient fuel flow for sustained max rpm climb out)
- clean the pistons on each carb and ensure the up and down movement (finger in the carb throat) does not have any friction.
- what's the venting system on your fuel tank ? could that be blocked ?
- you could have bad fuel, empty the tank and refuel.
The variation in power at your full power test is not normal