what size turbo should i go with my 06 silverado im going 3 inch piping and rear mounted and intercooled im doing everything my own everything is stock

Im not sure what size turbo you should really use. A lot would depend on how much boost you want to run. Why intercool and rear mount it. One of the big advantages of rear mounting is your not sucking up hot air from the engine compartment. If your keeping everything stock, I wouldnt run more than 5 to 7 psi, so a smaller turbo would suffice.... Better yet just by the STS turbo kit designed for the silvy

well im planning to get bigger injectors and a fuel pump and get a good tuned for now and i would just like to get an intercooler cause it would look cool behind the grill right.

Just because it looks cool doesn't mean it is worth the money spent. An intercooler just means more parts to break down. Like Bigbadram said, if it is rear mounted the Turbo does not need to be intercooled.

and for the money saved on the intercooler you can purchase a moderate nitrous kit

he wanted to install an intercooler for looks... doesn't sound like money is a concern...