[SS Tim]

Interesting variation. The only Custom Deluxe specifed to have headliners were Suburbans. The fact that yours has one could be explained any number of ways. Does your truck also have a cargo lamp? Is the headliner mentioned on the SPID? Maybe an A or X code. Would it be possible to see your SPID and build date?
Personally I'm thinking a body misbuild where the incorrect inner panel was installed during cab assembly. Likely it was signed off and a headliner was popped in off line. If it has the cargo lamp as well I'd say it was an incorrect build schedule. But the fact is headliners were not part of the Custom Deluxe or Highlander pickup trim options.