What's the difference between the 2003, 2004, and 2005 Z's, when only referring to the base model?

I think that 2003, 2004 and 2005's are all the exact same engine, exterior and interior wise but also in 2005 there is a limited edition 35th anniversary version with 300 bhp instead of 287bhp or whatever it is.

On the 2005 model a lot of problems that 2003 and 2004 models have been having will be fixed. Like the transmission, electronic problems, and the like.

Yeah, the 2005 base models should have no problems. They also have wideband O2 sensors instead of narrowband O2 sensors which were used on 2003 and 2004 ECU's.

Also, there are some other small things like all come with heated mirrors and etc.