I know this subject as been discussed before, would just like some more info. I have an 06 supercrew 5.5 box. It as 275/65/18 on it. I want to keep stock wheels. How much bigger can i go without a lvl kit? With a lvl kit? i was looking into putting 35/12.5/18. What will this affect? speedo? brakes? power? gas mileage? Also like to know where and how much can i get the Harley grill? I also plan on installing the Edge, cold air intake, and muffler for now. Can ayone recommend a great sounding replacement muffler?

 

You should be able to fit 33" tires w/out the leveling kit, but with it you should be able to fit either 305/75R18s or 315/75R18s (which would be 34 or 35x12 or so, depending on tire manufacuture).
I think it will affect your speedo, the brakes should be fine, you will feel a power lose(expecially when acceleration) and that why it would be good to have 3.73 gears, or regear to get the power back, and your gas mileage will get worst, do to the larger rolling mass, and the tires would change your effective gear ratio.

Harley Grill?
As for mufflers, it's usually out of flowmaster or magnaflow, and I'd prefer magnaflow.
I personally put a cherry bomb Y pipe exhaust system on my Dad's 04, and I think it sounds 10 times better than a flowmaster, and alittle better than the magnaflow, but alot cheaper than both.

 

Only part I can help with is unless your truck has at least 373's you will feel a lose in power with the 35's and will feel a little with 373's. I have 35x12.5x18's on my truck and it will change the speedo it will make your brakes feel a little weaker then original and you will lose about 2 MPG with the bigger tires. You can fit 35's with a leveling kit if you stick with the stock rims with little rubbing but with after market wheel it wont work because of the offset.

 

Look on ebay for the Harley Grill, I saw some on there before