I agree with SPRINGFIELD_XD_40 and I would add more. Check your grounding, clean contacts on engine grounding will also restore the electrical system, an additional grounding path, at least 5 points, will surely help. Another important thing that is usually not performed is cleaning the fuel lines, replace the a 1 year old fuel filter with a new one and check your air filter and clean it kung kinahanglan or better replace kung replaceable type. Next is cleaning the engine internals, an engine oil with good detergents can help clean the cylinder walls. Kabantay ko naa nay mga interesting products karon sa True Value ayala, mga engine cleaners. The last but the best as what I have experienced and others who did an engine treatment is have your engine a metal ceramic coating to rebuild itself to near factory spec while you're using it. During the engine treatment process, your cylinders are cleaned and will become more slippery. I'm talking about RVS -
http://www.rvs-tec.com/English/product.htm, I am not selling it but I applied it on my engine and restore good engine compression, better performance, hilom ang andar ug responsive na kaayo than the first time I have the car nga wala pa nag cleaning ug nag engine treatment. I did it myself pag replace sa air filter, spark plugs, grounding and engine cleaning one at a time mao makaingon ko nga there's a positive effect in each step. Changing of oil (<-depende sa klase sa oil but usually every 5000km as recommended sa manual), radiator coolant and transmission gear oil (<- every two years ni, kalimtan ra ni sa uban) ra ang gipatrabaho nako sa Caltex Banilad.
Considering everything suggested sa tune up was done right including above ug wa gihapon ka ma contended, maybe that will be the time you need to spend more for that intake, header and exhaust replacement or a more powerful engine that can meet your required power.