wishin

My 2004 Silverado with the 4.8 engine now has 127k of "normal" driving. The auto transmission shifts like it did when I left the showroom. I changed the trans fluid (only that which was in the pan) at 60K and am now debating a trans oil & filter change, along with scheduled fluid changes at subsequent 3K intervals thereafter, to totally replace all the old fluid after 4 changes. A local shop trans repair shop advises against it, saying it may lead to problems.. (They may have an ulterior motive.) Has anyone here experienced a problem after such an action? To be clear, I am dead-set against a flush, as opposed to an oil and filter change, so will not entertain that idea. I thank you in advance for sharing your thoughts and experiences in this regard.