Will not shift out of 1st

I talked to a tranny guy. He suggested putting it i reverse at 15 mph to free the governor if it was stuck. I did this 4 times w/ no luck.

I have to drop the trans to get to the governor due to the tight fit in my car so I decided to pull the valve body out before dropping the trans. It looks to be fine. All of the balls are in the correct spot. The valves are free. I haven't removed the valves yet. The only thing that looks wrong is the 3/8" ball and spring is missing. The manual I have refers to this as a high pressure relief valve. What does it do and what happens if it's missing? When the trans was rebuilt the guy put a shift kit in it. Would a shift kit call for removing this relief valve?