When using a macro to use an item or slotid the tooltip displays the correct item but with it's base ilvl, not the ilvl that item actually has.

Example: when using "/use 13" in a macro to always use the first trinket slot, the macro works as intented but the tooltip is displaying wrong. My ilvl 184 mythic trinket is displayed as the same item but at blue quality with an ilvl of 158 which is the base version of that item dropping in normal dungeons.

In case anyone anyone comes across this issue, in the tooltip-functions.lua, replace GameTooltip:SetItemByID(data.Id) on line 12 with GameTooltip:SetInventoryItemByID(data.Id)

Interesting idea. I suspect that it may still show the wrong item level if you have 2 of the same item but different item levels (it'll pick the first one it finds).