[Jonboy]

I bought a 2001 ECSB with a 5.3 in 2003, and my buddy bought a 2003 RCSB with a 4.3 at about the same time. My 5.3 truck had more power and got better mileage. I am pretty sure mine has 3.42's in it, not sure about his. This might be apples and oranges to your truck. I think I would go 350, especially if you already have it.