There were some dogs on the programme who weren't stressed and the study itself was very lacking. There was no correlation on how many of the dogs involved were rescue dogs, what breeds they were and what category of breed (eg working vs show, hound, terrier, toy etc) how many people worked, how many spent almost all their time with the dog, what socialisation they had.
It would be very interesting to know what was different about the dogs that didn't have high cortisol levels. I would hazard a guess they were the ones that had a good, secure starts like the pups on this list, who had owners that got them used to being left from as young an age as possible.
Mintchoc, it does sound like he's tired, but too hyped to settle himself. You could try teaching him 'settle', basically just repeat the word in a soothing voice every time you catch him settling down or napping for a few words. So "Settle" then immediately "Good Boy". Alternatively you could do a bit of what they did on that programme and get a rug or mat and train him to settle quietly on it. You just reward him for going on the mat initially, then for sitting on it, then lying on it, then extend the length of time he's on it and eventually only rewarding him when he stays there quietly for a period of time. and might be helpful too.
We've been out for the day to visit my sister today. It involved an hour's drive in the boot of my Mum's car with Lurcherboy. We'd steeled ourselves for him to yell, but after a minute or two of whining he shut up and was quiet all the way there. 
Our crate doesn't fit in Mum's car, so both dogs were attached via there harnesses to anchor points in the boot. Unfortunately, I failed to realise that Pip had his long lead on and at one point he half climbed over and ended up sitting on dd's head. Fortunately, he did listen when I told him 'off' and he didn't try it again.
Puppy classes tomorrow and I'm ridiculously nervous.