Solid lifter on hydraulic cam?

Hi 340mopar- The springs were new and matched to the cam ,933 hemi spring with 284/484 MP cam. There`s less than 600 miles on the set. I did have 3 lifters that wouldn`t pump up correctly from the start. They were removed, cleaned, and replaced after which there were no more issues with them not pumping up. After talking with techs from all over ,their collective opinions seem to be that perhaps what I`m experiencing is not valve float but a restrictive exhaust(since I`m still running the exhaust manifolds) the MP tech being the only one not of that opinion. I`m not a big fan of headers although almost every muscle car I`ve owned has had them. I may relent and put headers on(certainly couldn`t hurt) just to see what difference it makes and go from there.