Line 2e of Form 1116 (foreign tax credit) does not exactly match with my gross income on Form 1040 - anyone know what might be affecting that?

Bring up the f1116.  Scroll down to the "Gross Income from all Sources Smart Worksheet."  Put the pointer over the entry. Right click.  On the box that appears, click on "data source." 

Another box will appear displaying the sources for the entry.

Thanks for the reply! I'm on TurboTax Premium, the cloud version. I don't see this as an option. Is there a way to view the same thing on this version?