This is a great treatment. The guitar sounds great, the vocals are fine, the string arrangement is well done, and there was a cool vocal surprise towards the end. The lyrics flow well and manage the musicality of the song.
So the ingredients are all there for something magical.
You noted that the vocals need help. Perhaps at the start of the song they were a bit tentative, but they seemed to settle as the song went on.
What I feel most though, is that maybe you've pitched the song a bit low, and you've been pushed into a part of your vocal register where there is not quite as much intensity and energy.
I would really like to hear this song taken up into the 'high torque' range of your register, maybe as drastically as putting it in G instead of D. You don't need to sing more dramatically, because you don't want to lose that lazy, laconic feel, but I think that singing it a bit higher would inject a bit more adrenalin into and provide for more vareity in the voice.
Nice work!