2000 K2500 454 173k miles

Just need a few more answers on this subject. I've decided to give a cleaning one more try before I have to tear down the engine. So question 1: Should I try Seafoam in the oil or ATF? I am leaning toward Seafoam. How long should I leave it in? 500 miles? Right now I will have to drain some oil out because it is a quart overfull with the other additives that I put in already.

Question 2: Do the lifters need to be replaced or can they be cleaned? What causes them to go bad? Do they get dirty and just stick in the cylinder or is there a seal inside that leaks?

Money is tight, but I need my truck. If I need to replace them I will. Any help is appreciated, Thanks in advance. Andy