Lowering advice

[04CrewCabSTL]

I want to go with a DJM calmax kit. I was thinking about a 4/6 but this is my daily driver. Im worried about going to low but also worry a 2/4 isnt low enough. I want to keep as close to factory ride as possible, thats why i want a calmax kit. My other concearn is my wheels, i hace american eagle 20's, i was going to get smaller tires but was worried about clearence. I see alot of trucks with a 4/6 using 18's. Any input would be greatly appreciated.

[ABQFirefighter]

What size tires are you running?