how do i know if i need to adjust my valves? my truck is a 96 4x4. 186000. no idea when they were done last, i bought the truck in march with 169000 on it. it seems to be running fine, but it sounds a little rougher than usual. i'll be doing some other maintainance this weekend, and was wondering if i should do the valves. if so, how hard is it? i have adjustable rockers on the hot rod, so, i know how to do them on a gasser, is a diesel different?