Check your spatial index on the feature classes that you are drawing. if it is a bad index it may have to fetch all features every time you pan/zoom. You can verify a "bad index" by doing an identify on a feature and see how long it takes. If it is not quick then it is a bad index.
In ArcCatalog, right click on the Feature Class and select Properties. In the Feature Class Properties window, select the Indexes tab. Towards the bottom the Index GUI, select Recalculate for the Spatial Index. It will update the Spatial Index for that feature class. There's also a tool called Calculate Default Spatial Grid Index in the Data Management toolbox -> Feature Class toolset.