Jeksdad

So here is the run down. I rebuilt my 95 XJ 4.0 l at 296,00 miles, 6800 miles ago and lifters started making noise. I checked for pressure (Hwy speed 2000 RPM 50 PSI cold and 30 ish hot idle ) and flow both are fine. So I pulled the lifters and cam and they are both shot. After checking spring tension and oil passages I replaced both cam, lifters, timing chain and gears. Primed engine, used assembly lube on everything fired on first crank. Replaced the 10W-30 and added ZDDP additive. Lifters clattered for a brief moment or two and then all was good. Ran engine at 2000 RPM for 25 minutes, checked all fluids and went for a ride on the hwy. Three days go by and I am getting lifter noise again.
What now???