Hi all I have a 1999 suburban with 163,876 miles on a 5.7L i have a 2 problems frist is when I start it in the morring it knocks a little and some times the liftters tap till I put it in drive but I have good oil pressure but when I drive it for like 30 min and come to a stop the oil pressuer drops to 0 but it is not knocking or taping I am concernd about the knocking do I need a rebluid or do you think I can get away with and oil pump in it thanks