I put it into gear and it dies.

So I recently swapped in a 318 with a 904 into my 1970 duster.

What is weird about it is that it fires up and idles at around 8-900 rpm and revs out and runs good in park. Whenever I put it in any gear, it dies almost immediately. It shifts pretty hard into gear and makes the car lurch a little bit.
I rebuilt the carb and tuned on it and it still does it.

Any ideas? I'm at a loss and so are my other mopar friends

*I don't have a kickdown linkage, so I put a spring on the trans so the kickdown bracket thing on the trans had pressure on it.
I took that off and it did not change anything.
But could the problem be a result of not having a kickdown?