78D200

its probably a BB 727. Best thig to do is look at the fluid and smell it. If it is a brownish color and smells burnt, then the tranny might need a rebuild (worse case) or the fluid might just have to be changed (easiest fix). If the fluid is burnt or it is fine, you should still drop the pan, that will tell you a lot about what is going on inside.

If the fluid is burnt and the filter is dirty, a simple tranny service (new filter and fluid) might fix the problem. If that doesn't then you will have to pull the tranny and have it either rebuild or replaced.

If you drop the pan and the fluid is good, but you notice a lot of metal shavings, then there is a good chance the clutch packs are worn and the tranny will need to be gone through to see if a rebuild will be enough or if you will need a new tranny.

You will also want to get a new torque convertor and flush out the tranny cooler and lines if you need to perform a rebuild or replace the tranny.

Sometimes rebulding a tranny is more expensive than just replacing it.