Th350 shifting issue

Hey guys, I just picked up a v8 swapped s10 with a th350 trans which runs really good, until. I came out of the store earlier and it would not shift on it's own. I had to manually shift it up and down to get it home. The automatic part was completely gone. However, shifting manually was working perfectly.
I'm not familiar with Chevrolet nearly as well as I am with ford's, but I do recall people talking about Chevrolet transmissions doing this and how to fix it. Just so you know, this transmission is supposed to be new, and it does look the part, as does the blueprint engine.
Thanks in advance, Skip

 

Vacuum modulator or vacuum line to it?

 

Thanks man, I'll start wrenching on my new to me and first one in probaby twenty years, Chevrolet, first day of the new year! Haha. I really don't mind. At least it has an engine in it, unlike my ford!

 

Lucky Man!!! First day of the new year and you get a Free Manual Shift Kit

Actually the governor could be sticking .
On a '350 this can be removed from the trans easily from the drivers side

 

This video will give you an idea of what to check for if the governor is sticking.
Fast forward to 1 minute 16 seconds

I would not use a hammer to pull the governor cap, use a flathead screwdriver.

When you pop the cover off be sure to have a catch can. About a half quart came out when I pulled mine about a month ago.

 

If it’s new to you, while you’re under there with the drain pan, might be a good time to drop the pan, do the filter and have a look around.

 

It just seems funny to me, the transmission looks brand new, the guy said it was brand new I don't know why it would already have a problem. It has a warranty, but I would rather just make the damn thing work.

 

It wont take you 30 minutes to check the modulator and governor, maybe an hour from start to cleanup.

 

Transmission shops used to have rebuilt governors ready to go circa 1986.. not sure if they still do.

But my vote is for the governor!