It's hard to imagine that fast-growing annuals like tomatoes might be suffering from transplant shock, but it's possible. They're devoting their energy to establishing their root systems before sending up a lot of new top growth. Be sure you're watering deeply when you water, so that the roots are encouraged to go deep. I like to set the sprinkler on mine and run it for an hour. With deeper watering, you can get away with watering just once or twice a week. Mulch your plants to conserve soil mosture. If you can add a layer of compost for mulch, the plants would love it. You might also consider using a slow-release granular fertilizer so that nutrients are readily available when the plants need them.