Do yourself a favor and buy the OEM mirrors if not new then from a wreaking yard! Having bought after market mirrors that came from China I sent them back and ordered the from the dealer!
There are some aftermarket towing mirrors made in Canada. They make most of the mirrors for the big three. Look on Ebay and make sure that in the description it says made in Canada. With all that said I went to Ebay and could not find one OME mirror or OEM mirror.
The issue I had with the aftermarket mirrors was the mirror itself would flex distorting the image. I could fix this by quickly moving the mirror back in the opposite direction to flatten the mirror back out. The motors were also very loud compared the the factory mirrors. They were sent back for a full refund + all shipping. I would make sure whoever you buy from will pay the return shipping if you are not satisfied. I bought from 1A Auto and they let me return the mirrors without any hassle at all!
If you do buy them and they have the turn lamps that need wired up make sure to install the mirrors, put the door panels back on and test the mirrors BEFORE you do any extra wiring! This includes driving the truck to make sure the mirrors don't bounce around driving at highway speeds. Drive with them pulled out like you would towing. If your happy with them you can remove the door panel and finish the wiring. This helps both you and the supplier. You because if you don't like them you save the time of having to unwire them. The supplier because he does not have to return them to the manufacture or pay for a new wiring kit. In the end both of you win.
Don