how can i get my car to run as best as possible

my truck is leaking oil from the rear and front crankshaft seal due to vibration from a vacuum leak i belief. i fixed the vacuum leak, but since i will be repairing it myself and will have everything apart i want make sure i check everything possible that i can,maybe even improve it, with performance parts if possible or just some pointers of the vehicle i should check. how can i get my car to run as best as possible.what are some major compartments to go over and check. how can i increase the power