My new Comp Cam lifters do the same thing. I made sure the rockers are adjusted properly, good oil pressure and flow to the heads, etc. I also found that they pump down in less than a couple hours by pulling a valve cover, pushing down on pushrods, and rotating the engine around. Every time it sits for a couple hours or more, I need to let them pump up before driving off. Otherwise it runs great when it's warmed up.