2003 hemi getting slow and poor mpg

hey guys need some help here I've owned this 2003 dodge 2500 hemi for about two months now and it been getting slower and getting reel bad gas milage lately i popped the hood to check oil and all the fluid and saw that my coil packs are getting old looking and look like some are stating to split apart. it also looks as if the plugs and wires are all original along with everything else under the hood. i am looking into the MSD ignition for this rig and need input on if I'm gonna notice anything from doing this up grade?