I have an unusual problem with my F250 triton V8. The engine seems a bit low on torque (can't really tell) and it started to "consume" sparkplugs every 15k miles. The plug electrodes appear white and erode quicker than usual. I've had a trusty mechanic check it out and it's not throwing any codes. Any idea what could be causing this?, bad lambda sensor? On a side note, the truck is getting good mileage.