How much wind were the tomato seedlings exposed to before transplanting outside? Wind strips away moisture, breaks plants, cools the plant lower than still air tempature, carries abrasive dust, stresses the tender seedlings. Just like skin, plants can get wind burn, then there's altitude to consider, UV at 7000+ feet elevation is much stronger than 1000-2000 ft elevation, and can really stress tender seedlings
1. As a test - ask a local friend to give you a tomato plant.
2. cut a gallon plastic jug so it's only 75% as tall as it used to be, put 1-2 inches of gravel in and and fill with water low enough to not go into the inner jug.
3. put ink or dark food coloring in the water so it will soak up heat better
4. cut a 2 quart plastic jug short enough that if is 2 - 3 inches below the top of the other jug, and put potting soil, and the new tomato plant in your homemade solar heater water container.
5. put a weighted top with holes in it over the top of the inner jug. Or use a layer of dried weed stems as a shade, gradually removing stems to allow more light.
6. every 2 days make more holes to let in more light
After a week to 10 days the seedling should be acclimated if wind, and high altitude UV were the problems.
BTW when planting in the garden work some sand into the dirt where planting, the silica from the sand helps build stronger tomato stems.
A lot of strong light on tender skin ='s sunburn, a lot of strong light on tender plants too fast = 's sun damaged leaves. ( like my transplanted irises
) 90-95% cooked for this year. went from heavy shade to a bright sunlight spot and once the rainy days quit - ZAP ! Woops - too late.