Simple question, i dont wanna order anything until i know forsure that my stock head unit will support subs? its a 2005 1500 slt with the infinity system, if that helps. thanks guys.

 

It will if you add RCA cables to the head unit which is something else you will have to buy and add in yourself (or the shop).

Why not get an after market HU though for better sound?

 

You will need two things. A line out converter and a bass restorer such as RF's DEQ? or a JL cleansweep. I believe both those units will do both of wha you are looking for. Stock HU destroys any bass output a sub would want and need. It'll suck if you don't get one of those units. You could do the RF 360.1 but those are pricey and take a bit of tuning.
You could get away cheap with just a line out converter but it WILL not sound right.