Invoice Pricing and Getting the Best Deal on a Truck

My workplace has an employee perks system where I can get invoice/employee pricing (it’s worded either way with each dealership)

The brands I can get this from:

There are about 6 different dealerships that offer this and I am more in line with the Nissan Titan Pro4X and Ford F150 XLT or higher trims due to the modern features that the Tundra just does not seem to offer for the price point.

I am very new to leasing and reading up on all of the information but want to know the best way to use this special pricing when going after a new lease and getting a good deal like I see on these forums.

Secondly my current car is worth around $1k more than my financing on it; would I be better off using it as trading in when I get the lease or looking to sell it at carvana/vroom/dealership? I always read and get told that dealerships never truly give you what your trade in is worth and don’t want to get hosed on that side of things.

TLDR: I get invoice pricing and want to know how to use that as an advantage when setting up a new lease or if invoice pricing may not be as good of a deal as some of these discounts off MSRP I see posted.