engine cutting out when engaged into drive or reverse

[mad dog]

hey guys someone has hopefully had the same issue got a 71 charger with 340 4 barrell holley
starts up good as idles sweet when put it into reverse or drive it cuts out any suggestion
just got the thing on the road has been running ok just started happening would be grateful
of any help:confused2:

 

[Coronet 14]

Is the idle set too low in gear, Vacuum leak