Galion T-500 Grade O Matic

I have a Galion T-500 Grade O Matic . I am trying to find out if they used the same transmissions in the Grade O Matic's and what type of transmission is in it. Also need to know what type of fluid I would use? I can drive it in high speed, high range but the slightest hill will slow it down to nothing. Same thing in the high range low speed. Any help on what to look for. I have a Case tractor with the Case O Matic that acts the same way when it's low on fluid
Thanks in advance
Rick

Galion T-500 Grade O Matic