Advice for a picky eater?

I'm looking for advice about feeding my picky eater.

First, some background: He's about 2-3 years old. I got him from a rescue in Feb, so I haven't had him long. He's a mutt, probably mostly Ridgeback with something else mixed in (perhaps Pit or Rott or possibly GSD). He's about 65 lbs but the vet says he should be more like 70 or so.

He's a wonderful dog, calm in the house, playful outside, very obedient in just about every situation. He loves exercise. In the morning before breakfast, we play chase and run. We take 10 minute potty walks throughout the day. And once a day we take a long walk, about an hour long. I walk 3 miles in that time, but with all the running back and forth and sniffing he does, he travels much further than that. This seems to be just right for meeting his exercise needs.

The problem is that he's a very picky eater. The shelter warned me about it, and it's been a struggle. Some foods he won't eat at all. Other foods, he'll eat for a few days and then stop. Foods he really likes, he'll eat for a week before he refuses it. To some degree, it works to alternate foods, feeding him something different every few meals. But that doesn't always work. I know about the recommendation to leave the food down for 20 minutes and if he doesn't eat it, to pick it up and not offer it again until the next meal time. I tried that. The end result was that he didn't eat for 3 days straight. The vet told me to basically feed him whatever he's willing to eat, whenever he's willing to eat. I started out with dry food because it's my understanding that it's healthier for them, but he started refusing to eat any brand, whether it was dry or soaked or had yogurt or meat broth or something else tempting in it. Now I've resorted to canned food, but he still refuses on a regular basis so I have to switch around. Sometimes, I can't get him to eat anything. He's been examined by at least 2 different vets who say he's very healthy. It's not an appetite problem -- he has an appetite if you give him the food he feels like eating that day. I also considered making him meals with groceries instead of a prepared dog food, but he occasionally refuses people food too, like some meats and peanut butter.

Anyone have any advice about my picky eater?

The other question I have is related -- some foods have an obvious effect on his energy level. Unfortunately, it seems that many of the foods he likes cause a drop in his energy level and many of the foods he doesn't like so much give him more energy. It's not nervous energy. It's "I feel so good let's go play" energy. It was always my understanding that a food that gives more energy is better while a food that decreases energy isn't good. Is that true? Not only is it a challenge to find foods this dog will eat, I have the additional challenge of finding foods that don't drop his energy level.

Am I right to avoid foods that cause a drop in his energy level, or is that not really an issue for his health?

Some foods that dropped his energy level: Pedigree canned food, Purina Moist and Meaty
Some foods that raised his energy level: Solid Gold canned and dry, Chicken Soup for the Dog Lover's Soul canned, Nutrish dry

Thanks so much for any helpful advice and experiences anyone has to share!