Outline Cells in Red That Vary by More Than a Value of 2

On the attached spreadsheet, five values are entered in cells B4-F4. Conditional formatting is set up to highlight a cell if the value is below 6 or above 9. I'd also like to set up conditional formatting to outline cells in red if two values vary by more than 2. For example, if the entered values are 5.5, 5.4, 6.2, 6.8, and 7.5, the 5.4 and 5.5 values would be highlighted for being below 6. I'd also like the cells containing 5.4 and 7.5 to be outlined in red because the difference between them is 2.1, or greater than 2.

Thanks for your help and quick reply!