One possible cause of a delayed Reverse in this transmission can be a stuck Low/Reverse servo control valve, which is located in the Low/Reverse servo. The Low/Reverse servo control valve controls oil flow to apply the servo. When the valve sticks it cannot regulate and fills the servo very slowly, causing the delay.
Because the valve and spring are located under a threaded end cap they can be overlooked. If the servo housing was put in a hot pressure washer for cleaning water, soap and dirt can collect in the bore and valve area.
Always remove the valve and spring during cleaning and double check that the valve operates freely in the bore when clean and dry.
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