New lifters won't pump up

I recently took my dart out to the drags and lost a couple of pushrods in my 440. Turns out a couple of lifters were stickking so I bought a new set of Lunatti's from Summitt. They seem to be of good quality. I soaked the lifters overnight then set up the lifters with 1/2 turn of preload past 0 lash. I ran the motor for about 5 minutes and their seemed to be a lot of clatter from the rocckers so I pulled the valve cover and a couple of lifters seemed a little soft. Should'nt they be pumped up after 5 minutes any advice would be helpful.