Hello- I recently purchased a 1997 full size silverado 350 vortec with 127000 miles. The truck was in like new condition. All highway miles with regular oil changes using havoline synthitic blend oil. I changed the oil using a pure one filter and had very slow oil pressure pick up at starting. The valves would clang for a few seconds. I droped the oil again and changed to a napa silver filter with 10w-40 motorcraft oil. Then no problems- instant pick-up no clanging of the valve train. Previous oil was havoline 10w-30 chevron type, with the pure one filter. Question- Do you think I am using the right viscosity for this motor with this mileage? Also, what do you think of the motorcraft-conoco oil. Seems to be excellent stuff. Any thought would be appreciated.