lately i've noticed that my truck has a very slight idle cycle... like you can almost hear the crankshaft hitting the bottom stroke and coming back around... no noticeable change in rpm's on the tach, no smoke or loss of power of fuel consumption... i changed the fuel filter appx. 3k ago, and use stanadyne fuel conditioner... i had the # 6 and 7 injectors replaced prob. 5 k ago... but no other probs whatsoever, any ideas or is it normal??