help please....still broken

[72sleeper]

this is pissin me off ive posted about it many times and i cant getit fixed and my dad is so lazy, but anyways my c10 when i first start it it runs fine but after about 10 minutes it starts to miss and my oil pressure gauge starts jumpin and i have to put it in nuetral when stopped so it wont die on me and i thank yall for the help but ivechecked the valves there fine(and if it was the valves wouldnt it be regularly missin instead of verysparatic?) and ive put in thicker oil (15w50) then that didnt work so i put in lucas oil thickner didnt work either, im thinkin it has to do with heat cause when my compartment is cool its fine but when i drive around for a lil it starts to do it after the heat builds up so any help would be great thanks..............