Bad Fuel Injector ?

I just got my truck back from the shop for new HG's, studs, egr cooler, oil cooler and the other normal "stuff" After the shop had everything put back together they found the # 3 injector appears to be bad. I decided to take it home because I needed the truck and figured I could fix it myself, since they were going to charge me a little extra anyway.

So first it runs rough at idle and low speed, then smooths out as rpms go up. It seems to do much better in tow/haul mood than normal because of the increase in rpm's.
I get codes PO267, PO269.

Is it OK to drive it with a bad injector for awhile?

How big of a job is it to change the #3 injector?

Is it really an injector or could it be wiring or something else?

I think I will order an injector(I'm sure I will need one at some point) then
wait to see what everyone here thinks before I change it.

Thanks,