sorry very unclear on what youre asking, i use the same 4.3L 4l60e tranny behind a 6.0 and besides rebuiding tranny and other issues it works fine, so youre saying with a tune it doesnt rev pass 3500 rpms? is the tune a custom street tune or mail order tune/ what kind of tune is it? is there any mods to the 5.3? is it stock ?