Question
Mike,
I planted Better Boys mid-May.  I added tomato stake fertilizer, mulch, and some topsoil to each plant.  The plants look beautiful, dark green and sturdy,  but they are only about 6 inches tall  and are covered with golf ball sized fruit.  They have not really grown!  I live in Kansas City and we have received an abundance of rain in the past few weeks and temperatures have been averaging about 85 for the high.  

Answer
Tom, the plants are most likely recovering from the inital shock resulting from transplanting.  This is not at all unusual, especially in spring.

Here in Ohio, our tomatoes and peppers do not experience a growth spurt until late June or early July.  Since you live in a slightly warmer climate, yours should start perking up by mid-June.  The normal rule-of-thumb is six weeks following transplanting.

Otherwise, it sounds like you've done all the right things.  The mulch will help retain moisture, and the fertilizer, being a specialized tomato fertilizer, is high in phosphorus which will encourage large fruit and a large harvest.  All that is required at this point is patience.

Have a great weekend.

Mike