Gimp> Gradient text

Select Text Tool
Click and drag inside your image to size your textbox
Enter in the desired text
Select the Select by Color Tool
Make sure Feather Edges is NOT checked
Click on your text (make sure to get the colored portion, not just the box)
Select the Blend Tool
Select the desired Gradient by clicking on the image next to Gradient:
Drag your mouse from one point in your text to another,
the gradient will be applied to the entire area you've selected.

Note: The wider you make it the more color range you will get and the better your gradient will look.

See it all done!