I don't know it the ground you replaced would effect the apps voltage but it wouldn't be a bad idea to check it.
Do you have a manual or auto transmission? What speeds or driving conditions does the engine surge? Is the check engine light on or do you have any fault codes?
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2002 6-speed, 5 inch straight pipe, Icebox, Edge Drag Comp/Smarty. Isspro pyrometer, mechanical boost guage & electric fuel pressure gauge. FASS 95, Valair kevlar/ceramic clutch...