What kind of calculation did you do?
simple i take as reverence a Saturn IB with Centaur upperstage, brings 3023 kg in GEO
source: Saturn IB Payload Planner's Guide
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http://www.up-ship.com/drawndoc/drawndocspacesaturn.htm
the Fuel of Apollo SM is N2O4/UDMH = Isp: 290 sec.
the Fuel of Centaur is LOX/LH2 = Isp: 425 sec.
means the Centaur can bring 1,46 more payload as SM
so 2070,5 kg for Saturn IB with SM
under the presumption the Saturn IB brings the SM in a Orbit
were its fly in to GEO (two Engine burns )
but second burn need fuel, Wat SM has to carry with
Wat reduce the Payload under 1000 kg