Chevy or GMC truck with the 4L60e transmission losing 3rd or 4th gears before and after rebuild? There are multiple small areas that add up to cause insufficient 3/4 clutch holding capacity. This hidden leak -only when hot- can smoke 3-4 clutches after rebuild, even after all other small areas have been addressed. Shown is how I test the sealing integrity of the input shaft fit in the drum to find a hidden cause of 3-4 clutch failure.