Need some help figuring out what is wrong

You're right. It sounds like there's a big hole in there somewhere. I just can't put my finger on where exactly. I hear lows, mids and highs, but it's like there's a veil pulled over it. Very strange.

There does seem to be some high-end "sheen" missing, mostly from the vocals and snare as best I can tell - the vocals are as though "pssss" would be more like "pshhh", if you know what I mean, and the snare is fairly fat but is lacking some high end "crack".  I would also try backing out the tremelo "pad" or at least move it away from dead center - the mids/center area seems a bit congested. 
 
I like the song though - the vocal track in particular is very Geoff Tate-ish.   
 

ditto on the high end sheen missing.... There is also a hollowness or boxiness to the sound as if the EQ is pulled down in the low mids and bumped a bit too much just above that. This is in the vocal ranges.
 
Go back to a flat EQ  and bump the highs a bit to start. Sometimes when we are mixing and wanting it done, we get in a rush and the EQ starts to look like a mess. If things are properly tracked, most EQ curves should be relatively flat with gentle rises and falls where needed.
 
It's not sounding like it's a major fix needed, just some gentle pushes and pulls in the right places to get a full, clear sound.

As far as 'from the studio to the truck',
This is an age old conundrum. What it mostly comes down to is that you're not hearing in your environment correctly.
Has "Tracey Studio's" rooms been tuned? 
 
I don't think the advice above about 'adding' this or that will get you very far. I think removal of frequencies will go a lot further. except for possibly adding some high end sheen 12k up. Try to identify the problem freqs in your truck. probably lows and low mids. A lot of low information (55hz and below) can be removed usually which helps the higher freqs come thru.
 
Best I can offer is to look into HarBal or some other freq analyzer that can show you what you hear.

wookie: I can email you an mp3, where?

It just occurred to me: you might look into phase problems, too.

There's a wide upper mid that almost  hurts.  Sweep with your eq and find what jumps out and reduce.  Kick need more volume and punch .  Vocals are a bit washed into the mix.   Sounds like phase/flange which makes it a little weird on the ears.    Some mentioned phase.. could be

Ok, spent sometime this week...wondering if I am really hearing it anymore, I have heard this about a million times.  Hopefully this version is better....
 
http://soundcloud.com/bla.mire/iou-mix-16-03302014

if you had more of a bigger chorus in the track it would bring more of an emotion in your voice! just my 2 cents! good song.

thanks all! I think this version is much better than the first. I made changes based on all of the comments. I will give it a few days and listen and see what I think. 

I think this is sounding better.    I would still throw Channel Tools on the tremolo part though and widen it to fall somewhere between the vocals (center) and main guitars (L/R), and perhaps add just a bit of 2-4KHz or so to the snare for pop.   But yes, the blanket is certainly starting to lift.    
 

This all sounds nicely balanced to me.
The main distraction for me is all the vibrato.
Using it both on the instruments and your vocal seems over the top?
Just on your vocal would be perfect IMO.
Some other effect on the guitars? Wah?