Transmission Shifts Too Soon

[87darthvader]

Hi all. I'm having a problem with my transmission. Its a 200r4 out of a Monte Carlo (or so I was told). It had a rebuild done before I put it in my car. I made sure of that. The transmission has a free spinning stall converter. The transmission gets into overdrive by the time I reach half a football field or so. It shifts way to soon. When I shift it manually by hand, it goes through all the gears fine. Its a 1987 Buick Grand National. The motor has a mild build to it. Does anyone know what could be causing this problem or have an idea on how I can fix it? Any and all help is appreciated. Thanks much!

 

[Janis Transmission]

You might not have enough tv pressure or its a og valvebody they will shift way to quick for your combo

 

[TexasT]

There is a metal tag on the pass side near the tail. It has numbers n letters. What are they? Fixing some of the low performance and diesel valve body/governor combos is hard. Just easier to swap to a setup for your combo.

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