I didn't have a problem, I mean everything was super tight but the tighter the better to keep the creases out of the leather. I watched the youtube videos and attached the back first then the front then the sides and finally the rear corner hooks. That's too bad you had a hard time. When it was all over, I'm glad I'm not in the upholstery business as a career but the leather on my '07 looks a lot better and after 15 years the original was due for a replacement.

I looked at Katzkin leather which I have in my Jeep Wrangler but they were too expensive for a complete package + installation when all that I needed was the seat cushions.

 

I wish I could find a new oem cover.

 

Most upholstery shops use a steamer when installing to help with stretching/relaxing the leather. Also for headrests, a vacuum with a plastic bag over the foam is the trick for those to compress the foam. Getting the armrests off is a bit tricky. If looking for info like on Youtube, etc on doing it yourself, look for replacing leather on a Silverado, Suburban, Tahoe, etc as those are orders of magnitude more common and use essentially the same style seating.