Assigning functions to hardware

Hello, I'm a P3d user and really enjoying the software. I've also been using a couple of GoFlight panels recently, (RP48 and G8) I find that the control knobs do not turn smoothly in the simulator when I have to assign a control to a knob via FSUIPC. Is there a way to smooth this out? It can really jump around when trying to assign altitude or heading for example. The default assignments in the GF Config file turn very slowly so I opt for assigning via FSUIPC.

Also how can you assign functions to buttons that are not preset in GFConfig or FSUIPC, for example I can't find a VNAV function.

Jim