I used a cheaper alternative called Noico. I used their 50mil foil-backed product on the complete floor and as tiles on the a/b/c pillars. They make an 80mil product as well, and honestly I probably should have used that.
I then layered Noico closed-cell foam over the foil. This acted as a gasketing layer.
I finished up with a layer of mass loaded vinyl. This was the true sound proofing layer, and wow did it ever work. My exhaust is painfully loud and this really helped a lot with in-cab drone etc. The product I used can be ordered online from Home Depot. It is called DB-3. It is by-far the cheapest MLV out there.
Being a crew cab this took a LOT of work, but I think it was ultimately worth it. I just need to do the doors and firewall at some point as I still have a lot of sound/heat coming through them.
Oh - and don't forget to insulate the back cab wall. I noticed the greatest improvement in sound deadening from that, but then the flowmaster super 44s drone real bad so that is probably why.