can you convert a lq9 with the truck intake to a ls6 intake? if so what parts will i need? intake, fuel rails.....

 

Yes you can... What you said intake, rails, and I think the throttle body will work on both intakes.

 

is there any power gain from doing this? or going to an ls2 or ls3 intake?

 

Power gains would be in the +4,500 RPM Range to move to a LS6 over a Truck intake.

The Truck Intake can make better TQ (and some HP) in the lower to mid RPM Range.

One Area to watch out for in the swap is the Water Pump for the Upper Radiator hose, which will be in the way of the Car intake Throttle Body. Do a search on the LS1/LS6 intake swap on to a truck front Accessories or engine.