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1. You are correct that the Lions will not have a fourth-round pick. They traded it to Minnesota for the rights to draft Tahir Whitehead last season. However, there's a good chance the Lions will get a compensatory pick or two from the loss of Eric Wright (and maybe, MAYBE Drew Stanton).
2. You've probably already seen this, but my first mock draft of the year is at http://bleacherreport.com/articles/1473021-lions-2013-mock-draft-the-smartest-pick-detroit-can-make-at-every-spot
I'm all for trading back later in the draft, but this year, I think the Lions will do well to go BPA at No. 5. They stand to bring in a key piece (perhaps a much-needed DE), and thanks to the rookie wage scale, they won't have to break the bank with that player (a la Stafford/Suh), either.