C4 transmission passage hole, what is it? Help please.

I have a stock 1965 green dot C4 transmission with a Transgo SK4L shift kit. It has been fine for 5000 miles until possibly it was resealed by a reputable transmission shop.
I bought the car from a friend who is telling me all he can remember. He did not know about the not shifting problem. He told me he thought it was shifting from 1st to 3rd when it was cold.
The problem is it won't shift at full throttle. I have checked and replaced the governor and the kickdown is adjusted correctly. I have tested the vacuum modulator, it checks ok.
All shifts seem to be ok, maybe a bit high at light throttle.
  A few things concern me, it has a deep aluminum transmission pan but no deep pickup tube/filter. The other thing is in the pics, it is a vertical hole with a horizontal passage. It was plugged on purpose by somebody with gray silicone. I unplugged it but before I put it back together is it some sort of trans mod that I need to put back? It is located just ahead of the valve body in the center, between the pan gasket and the valve body.

I tried to post pictures but this site is telling me that the uploaded file is not valid: exceeded attachment maxsize (0 kb )

I can't seem to edit my post so more info:
The trans has 5000 miles on a complete rebuild and the fluid looks real good.

Hopefully these Photobucket links will work:

https://s212.photobucket.com/user/laveennick/media/DSC02969.jpg.html?sort=6&o=0

https://s212.photobucket.com/user/laveennick/media/DSC02968.jpg.html?sort=6&o=1

Thanks in advance.

That hole is no big deal , it is just a hole to allow any trapped oil between the gasket and pump o'ring

Might be time to look in the valvebody

Gregaust wrote:That hole is no big deal , it is just a hole to allow any trapped oil between the gasket and pump o'ring

Might be time to look in the valvebody

I agree.

I pulled the valve body today and checked all of the pistons for freedom of movement and they all checked ok. I then found some of the bolts were loose that holds the valve body together.
I took it for a cruise and it is shifting at full throttle correctly. It seems to upshift with no throttle correctly now too so I guess tightening the bolts solved the problem.
It now shifts at near 5000 rpm's with the stock governor which I will replace with my lightened one to get it closer to 5500 rpm's.
Also I think I will replace the Transgo SK4L shift kit with the Transgo 45-01 recalibration kit.

A big thanks to those who responded!!!!