Lifters raddling excessively loud,losing power etc.etc.

What is your question?

Has my cam worn out,making the lifters sing real loud,as if they are not oiling. The oil pump pressure appears find,but after driving for a few miles,the car begins to lose power. After the car cools down it will go on a few more miles before it start the process all over a again. Can you tell me if I need a top over haul job and about what it will cost to fix it.Need a response as soon as possible. Thank You! God Bless!!!!