Car is runing kinda funny, gas mileage is limping too.

Hopefuly tune up will help. I had plugs replaced at 60,000. Now its over 80,000. What do I need to replace ? Whires?Distributer? What is the aproximate cost?
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Dmitry
90' 300CE
17" Lorinsers RS90
Brulen mufler
Clear Blinkers