I received mine last week and started working on them thursday night. I got the bottom of the driver seat fitted with a little 1/2" foam added to plump it out. I noticed that using the heat gun trick to shrink away the wrinkles doesn't really work, as once the material cools it becomes baggy again. I molded some additional foam around the top portion of the seat, and tried to put on the top cover, but that's where things went pear shaped. One of the wire pockets started to tear from the tension, and I found the holes I cut for the headrest posts (it didn't come pre-cut) during the test fitting no longer lined up correctly once enough tension was on the cover. Then just when I thought I might be able to pull it off anyway, one of the rubber tethers snapped.
So now the question is, where can I get another of those tethers? I'd be shocked if toyota still sold something like that, assuming they ever did in the first place... I may need to buy a whole GT seat from pick n pull and hope it uses the same mounting straps. Or take it to an upholstery specialist and sell them a kidney to finish the job for me.
By the way, I, too, found the same issue with the headrest and contacted the seller, sending pictures and offering to send anything else he needed back. I haven't heard back yet but will keep folks posted. Had I been more patient, I may have had mine finished after he made the adjustments for yours.