The reason I asked about the intake port gaskets, is they usually only last around 40k miles. The replacements last much longer. Here is the TSB from Ford about it. Thanks
This article supersedes TSB 05-17-3 to update the vehicle model years and issue.
Some 2001-2003 F-150, 2004 F-150 Heritage and 2001-2003 E-150/250 vehicles equipped with a 4.2L engine may exhibit the malfunction indicator lamp (MIL) on with diagnostic trouble codes (DTCs) P1131 and/or P1151 (system too lean bank 1 or 2). This condition may be due to leaking isolator bolts/port gaskets in the upper-to-lower intake manifold mounting area. This condition is sometimes intermittent and may not be apparent on a warmed-up engine.
Refer to the following Service Procedure.