'99 Suburban 7.4 ticking

[Frayed Knot]

I have a '99 Suburban with a 7.4J that has what sound like an upper end ticking noise. The dealer has already replaced all the lifters and no change. They have also killed each cylinder one by one to try to change the noise but it didn't. Now they think it might be cam bearings but the truck has 25 PSI oil pressure. Anybody else ever had this problem? It has just a little over 100,000 miles on it.