2004 HPDI 300, started fine this morning. When I took off it ran like it was bogging down for about 4 seconds then it sprang to life. next time no problem, 3rd time bogged again. next 3 moves no problem, last move did it again. I run the right fuels and additives. Plugs are 6mo.s old. Does it sound like time to change filters ? If so aren't there (3) to be changed, and what should it cost. (I'm no wrench)