It looks like a nice truck and by appearances...and I say that carefully....it would probably be worth the $4000.
That said, I usually dismiss any amount of money stated that someone says they have invested in their ride. You have no idea what they spent it on and how they interpret spending or investing in the first place. ie: their labor? chrome plated bolts? $2500 sound system? $650 aftermarket steering wheel...who knows.
I also agree about the dubious 34000 mile angle.....not so sure about that....so unless there is a true easy to read, easy to follow paper and history trail, dismiss that as correct.
Back to the point....it looks like a pretty reasonable truck for $4000, well worth looking at.
Good luck and keep us posted!
Coley