How was the cam broke in. Does it have the right valve springs for the cam? If the valve springs have to much pressure it will destroy your cam overtime. Fore a mild hydraulic cam you should have no more than 330 pounds of open pressure. If you have to keep adjusting you you valves it probaly means your cam is going flat. When you install the new lifters vary the rpm 2000 2500 rpm to get a good wear pattern other wise you will be buying more lifters and praobly a new cam. Next time you have you valve covers of while the engine running check to see if the pushrods are spinning if they are not spinning shut it off that means the lifters are not spinning and that will cause your cam to go flat. Usualy if your lifter are spinning it will destroy you cam in a matter of minutes. So that is proabaly not your problem.