TN Visa Reference Letters

I have held several TN visas as a systems analyst in the last few years they started cracking down on that category and insisting on a BA in computer science so regardless of my years of experience and my BA they denied my visa a few years ago. Fortunately I just applied and flipped to an L1A visa and currently hold that work visa. I am in the middle of switching companies and positions and will be flipping back to an TN Visa with that switch and applying for the mgmt consulting position.

I have the years of experience and the BA.. I know the examiners at DHS like to see letters of reference does anyone have any idea of what they are looking for in these letters of reference?

Any help would be appreciated.

Heather