1998 bonneville lifters sticking

I have a 98 bonneville that I bought at an auction and I beleive it is a lifter or two sticking i can hear the tick from the center of the engine below the intake and some noise coming out of the valve covers. Has gm had any problems with this and if so what is the quickest fix for this. I added some additive to try and get them unstuck but nothing has helped. Also the ticking does go away eventually when it has been ran for a while and no it is not anything internal like a piston slap.

thanks
John Nore
Nores Body Shop

try a thicker oil

Try some Motor flush , 20w/50 and a bottle of Lucas