engein problems

have a 3800 non-turbo and every book tells me that it has to be a 95 year no outher engein will fit in it why is it?

it has to hook up to the trans and be compatable with the pcm. if another year won't hook up to the trans then it won't work. that year was the last year that g.m. used the 3.8 in a silho .