So I bought an upper from PSA a few months ago and when I first got it I kind of thought the front sight was a little off but because I put on a scope right away I never thought about it again. Shoots great by the way, but I wanted to shoot iron sights with it and that's when I really noticed how off the front sight is. I had to dial my rear sight as far as it could go left in order to be sort of close to zeroed. Not sure how to even fix it or what they do when they do fix it. Can anybody help me out here?

Remove the barrel nut and see if there's play for the barrel extension index pin in the slot.  If so, see if the play allows the front sight to be correctly oriented. If so, get a little shim stock or equivalent metal you can cut/file to fit and fill the gap in the index slot on the shooter's left.  I'd also suggest sticking a dowel rod through the FSB and providing some counter torque as you do the actual torquing of the barrel nut, just to make sure nothing gets compressed or deformed in that index pin area.  Make sure your shim is below the valleys of the threads.   Make sure that when you have the FSB centered the feed ramps (assuming M4) aren't misaligned and the bolt lugs can cleanly enter and exit the extension.  If there's any alignment issue there, your barrel assembly is the problem and not realistically salvageable unless you wanna go to a rail mounted front sight, in which case you still want to make sure the lugs and ramps will align while the gas tube smoothly enters the gas key/receiver hole at the same time the gas block hole and barrel's port are sufficiently aligned. Odds are it's not that far out of whack, but I'm just saying.

If the problem is that the index pin slot on the receiver is off-center rather than just sloppy, use a file to widen it on the shooter's right side a tiny bit at a time and as cleanly as possible until the FSB can be turned vertical.  I'd suggest a small round and flat needle file to get the profile right.  Still check the lugs and ramps, then shim as above.

IANAGS 

ETA: Oh, you could also call PSA , that is if you don't have experience or tools for dis/reassembling uppers and don't want to risk fucking something up or wasting the money to learn.  If you can afford a replacement, I'd dive in though .

I had this problem with an upper from them and they never called me back after numerous calls and emails.

Communication and turn around time are iffy, but they will take care of you.

I left them a message on their customer service page yesterday and I just got an email back from them. I'll let you guys know how things go, but so far they seem to be doing pretty well.

Velveteen, thank you for that! I had no idea that the index pin could even have any play in it on the barrel. I might have to find a vid on Youtube or something because now you've got me curious!

I'd be surprised if it had play on the barrel, I'm referring to the slot it indexes in being cut wide or off center so the barrel doesn't index with the pin and FSB top dead center at least after the barrel nut is torqued down.  When using an upper receiver block to hold the assembly while torquing the nut, the nut will tend to drag the barrel ccw to the shooter if there is any play in the index slot, thus your FSB will be canted left and your rear sight will need to be drifted left to cancel the error.