Is there any documentation from Mazda that they changed the suspension in any way from the 2003 Mazda 6i (2.3 L4) to 2004 or 2005 Mazda 6i (2.3 L4)?

 

Not that I know of. I know that between 05 and 06 the design of the front sway bar changed for the V6 due to the new oil pan & exhaust setup, but other than that I believe that the suspensions are more or less identical for all years. Also, I think that 06+ may have gotten a slight brake upgrade, but I could be mistaken there.