Garvacious,

What were the specs on the old pump? HP & service factor and/or model #?

What was your filter PSI before and after pump change?

With 1 1/2" plumbing, you could be sucking some air into the system if the suction is much higher than what is was before. It is unlikely that the pump is cavitating because it takes quite a bit of blockage to do that.

The Superpump has a low SF so it shouldn't have much more braking HP than your previous pump. Unless, there is a good reason to upsize the pump I would stick with the same HP or even lower. You might want to consider a more efficient pump such as the Whisperflo or even Intelliflo. They cost more up front but will likely save you money over the life of the pump.

As for the SWG, it sounds like the flow switch isn't making contact on low speed. Try unscrewing the switch and adjusting the contacts (assuming that is the type of flow switch you have). Also, orientation of the switch can sometimes make a difference. Make sure it is pointed in the right direction.