2001 Chevy truck 8 liter
 

I'm not sure of the exact size ,, this truck developers a mis every now and then and the shop says sticky valves, and that all the electronic stuff is working fine, is this a common issue and how would you fix it before more serious issues evolv, this one ton duelly exstended cab, has 82,000 on it, like nw???? Thanks for any help!!