can I swap out the 3 speed transmission for a 4 speed?

1989 CHEVROLET VAN
35,000 MILES
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my 1989 chevy 30 van chassis with class c camper on it has a 350 eng. 3 spd auto tranny seems like it is very high rpm at 55 mph and bad gas mileage too!, can i swap out the 3 spd tranny for a 4 spd and get lower rpm and better mpg ?? and what tranny would fit ? thank you
Jan 3, 2013 at 1:31 AM
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Hello,

Those transmissions are not interchangeable.
The bellhousing is different, so it won't just simply bolt on. It will likely require major modifications.

https://www.2carpros.com/articles/how-to-remove-an-automatic-transmission-rwd

Please let me know of any questions.
Thank you.
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Oct 16, 2021 at 10:40 PM