I'd dump and refill with fresh oil and a new filter after 1500 miles, but there's probably no harm in leaving it in longer. It would seem to me that if there's no appreciable change in 1500 miles, there's not much point in letting it stay in the mix.... if there is a change, it's best to get whatever dissolved gunk that has been removed - out of the engine.

Frank

I HAD THE SAME PROBLOME MY LIFTERS WOULD TAP WHEN WARM OR HOT THATS WHAT IT SOUNDED LIKE I FIGERED OUT THE PROBLOME AFTER 2 SETS OF NEW LIFTERS AND HEADS AND ROCKER ARMS LATER WHAT I FOUND IS THAT THE NEW PARTS I GOT HAD THE WRONG JET VALVE ADJUSTER BOLT IN IT. THAY WHERE TO LONG AND HITTING THE VALVE COVER WHEN THIS HAPPEND IT CAUSED THE INTAKE ROCKER ARMS NOT TO HAVE THE FULL UPWARD TRAVELL WHICH CAUSED THE LIFTER TO CALLAPSE DUE TO THE LIFTER HAVEING SHORT UPWARD STROKE AND NOT EXSTENDING OUT AS FAR AS THE LIFTER SUPOSED TO GO. AND I BURNED A COUPLE OF JET VALVES TOO AND IT DID NOT SOUND LIKE IT WAS A CLERANCE PROBLOME BETWEEN THE VALVE COVER.I FOUND A WITTNESS MARK ON THE INSIDE OF THE VALVE COVER IN THE BAFFLE I ALLMOST MISTAKED IT AS A SPOT WELD.I REPLACED THOSE ADJUSTER SCREWS ON THE JET VALVES AND THE OLD ONES WHERE A LOT LONGER ABOUT 3MM.AFTER THE CORRECT ONES WERE INSTALLED NO MORE NOISE AND RAN GOOD.AND NO TSBS FOUND ON SUCH A PROBLOME 2.6 G54B

i got tired of my hyd lifter ticking,that is why a few years ago when i got my clearwater head i got the man adjusters.i dont mind adjusting them every 10,000 miles and they are not as loud as most hyd lifters i have heard on the 2.6's out there.