Stalling when put in gear

[C20Chevy]

I recently purchased a 1970 c20 camper special that has been sitting for a while after the original owner passed away. Its has a 350 motor with a turbo 350 trans, I work at a car lot and put it on a trailer and brought it over. Have had it in the shop and gone over for inspection, everything good only thing is the truck has a little issue with it stalls when you put it in gear until it warms up. I've been able to move it around just keeping one foot on the brake and feathering the gas, and once I get it going it runs perfectly fine and i can drive it normally. Any ideas?

Thanks,
- Mike