I've been getting the UOAs for my 2008 Nissan Titan done at every interval. The high lead values keep bugging me. Its always had Amsoil Signature Series 5W-30 in it, along with an Amsoil filter. Oil change intervals have been right around 10k miles. The type of driving it sees is long distance commuting and the occasional very light towing. Do I need to be concerned? It seems to run just fine. Any suggestions on how to lower those lead values?