Hey, Steve. You might still try a 3" variable pitch pulley on your motor. They`re
not much more expensive in that size, and you`ll have some adjustment range. It`s just like a regular pulley, except one flange has an allen set screw. If you loosen the set screw and rotate the flange in a turn or two (the pulley hub is threaded, as is the flange), this narrows the pulley width forcing the belt to assume a larger diameter. You`ll get around 1/2" of adjustment this way. Not a lot of adjustment, but on the motor shaft it`ll obviously make the most difference, from 92 to 108 RPM or so in your 3" case. Try a 2" for some middle ground.
Good luck!!