Howdy Mluck:
What do yur plugs look like now? Are they whitish and/or chalky? Is the electrode purning away? If so try a step colder in the same type/brand as you are now using. If you change brands start with the reccomended head range for your engine then go from there by reading the plugs,
Typically I will use a one step colder plug in the summer.
Adios, David