Im looking at buying an 04 LB7 that has ca emissions, I was told to stay away from the ca ones. Whats the difference other than egr valve and cat? Is the federal better for mods?

Its the EGR, Cat and also the computer is very sensitive to everything and will set the check engine light. The EGR doesn't even work right and you will have EGR codes all the time. The only way to block it is with EFI Live or HP Tuners. Get the federal truck, it will run better, less headaches, etc.