I have 6 tomato plants out. Four of them are in one location and two are in another. They were all planted in mid-April. The four that are together show good new green growth but the bottom leaves are turning yellow and on one plant a few leaves have turned brown and died. The two planted separately have the similar yellowing problem but to a much lesser degree. I have insured that the plants each get at least a gallon of water per day; from God if it rains, frow me if it doesn't. Anyone know why and the fix?

I think you're overwatering. I do not believe that your tomato plants need that much water now, while temps are mild and rain is often. When it becomes 100 degrees outside, possibly. I know it's important to not let them dry out completely, when they have set fruit but they could stand to not have "wet feet" constantly.

Let them dry out a bit, then fertilize with Garrett Juice or Bioform. Clip off the lower limbs that are yellow or that might be touching the ground already.