harm it to do it now
i have 2003 trailblazer the trans has not been serviced in 150000 mi. will it on 2003 Chevrolet Trailblazer
your guess is as good as mine. good luck. how does the fluid look or do you have any shifting issues
No shifting problems, the fluid is brownish red, not red like it should be
IF you do anything at all , DO NOT flush!!! Only drain & fill (will probably need filter and pan gasket on that) With that mileage , I would strongly suggest ONLY FACTORY parts and fluid!!