Answer: I'd stay with the plants you have. Summer heat really reduces the ability of tomatoes to set fruit. New plants could be set out in mid-July for a fall crop if you like. However, your current plants (except "determinate" and bush types) could also be recycled! Here's how:
Take a shovel and remove a scoop of soil from a spot near the plants. Take the end of a vine, lay it in the hole with about 6" sticking out the other side and cover it with the soil. Water the buried portion well and keep moist for a week or two. After about two weeks, the buried cutting will have formed a root system, and you can cut the new plant away from the mother plant. Then you can remove the mother plant and resume care of the new one for fall. Be especially careful to check the plant for mites and aphids as they can be especially tough on a new plant in the summer.
Good luck with your garden!
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