2000 Chevrolet Suburban • 130,000 miles

5.3 engine starts in the morning and is quiet at idle for 20 seconds then it ticks like a collapsed lifter for twenty seconds then it quiets and never makes any noise until the next morning no matter how many times I start after that. The oil pressure seems like it is lower than it was I think it reads 38 with the engine warmed up at 60 mph and 30 at idle warm. I just had a new head gasket put on at the dealer and I had them put new lifters in at that time, the problem is still there, so I ruled out the lifters. I thought maybe the oil pump was losing its prime, but the noise does not start until it has run for 20 second, so I am stumped any ideas would be appreciated.
November 22, 2012.

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