Engine dies in gear?

[Broken65]

Hi all, I've recently put a new carb and trans in my 65 truck. Ran the truck to work and back (approximately 25 miles) with no issues until I got a few blocks from my house, the engine then began dying at stoplights. It started right back up out of gear until put in gear, if you give it gas it's fine in gear though.

I took it to my friends prior to the issue, they said it seemed good. All having 20+ years in the mechanical field. The engine runs great, slightly rich. I was wondering if anyone had this problem before, thanks in advance!

Some specs
-1965 chevy C10 1/2 ton
Engine-1966 SBC 283
Carb-new Rochester 2 barrel
Trans-newly rebuilt TH350 60's or early 70's
Vacuum-17-18hg in park, 20-25hg in park at 2000rpms and above
Dwell-30 degrees
Timing-8 degrees BTDC before connecting advance
Plugs-NGK with 35 thousandth's gap
Idle speed-700-800rpms when last checked