The smoother the operation, the less likely the wheels are to slip. Also, the more grip on the wheels, the easier they'll stick and gain the traction needed to overcome the friction of the cutter wheel mechanism.
When you rotate the wheels with the mower off the ground, does it take a lot of effort? Is the axle/hub rusted at all? Filing/sanding down the parts under friction should improve the performance. Failing that, sourcing wheels with extra grip, or modifying the current wheels should work.