How can I create a sales report on a per customer basis showing Sales, GP Sales and GP % for the last 3 years. 

You can create the above report by using the Pivot Table report from Market Analysis 

This creates the first Pivot table with Sales YTD for each customer

• Using Market analysis, create a customer list based on selected criteria
• Once your list is complete select File / Print
• Select Report- Excel Pivot Table. This report takes a long tome to generate. When the “Pivot Table toolbar” appears on your screen you are ready to begin report generation
• From the Pivot Table toolbar select Pivot Table/Wizard
• Select Layout
• Slide DivRef Name to “Row”
• Slide YTD sell to “Data”
• Select OK
• Finish

• Select cell D10
• Select Pivot Table/Wizard from the Pivot Table Wizard
• Select Next
• It will ask you what pivot table to use. Use the highlighted one (pivot Table 1)
• Next
• Select “Layout”
• Slide Div Ref Name to “Row”
• Slide YTD GP to “data
• OK
• Finish
• Hide column D (Div Ref).
• Create the GP % by dividing Sell by GP$
• Label Row 9 with the correct Labels ie F9 would be YTD GP%