A few months ago I picked up a bone stock 2001 4WD EC/LB DRW, 6 speed for 6k. To me, the mileage matters very little, and the one I picked up has twice the miles. At 15 years old, they need the same things. And its more likely to of been replaced with more miles, because the previous owner(s) actually drove it.
Things that matter to me, body work IE rust. Parts can be replaced. Body work takes a finesse I dont have, but I can repair the mechanicals. The interior looks pretty nice, but I am thinking thats a 6k truck too, being RWD. I would personally want to see it start cold, and check blowby, and see how it shifts.
If it was me, I would make an offer of 6, see where he's at. Then decide what its really worth to you.