th 350 problem?

[the general]

I have the following problem on my 75 k5 383,350,203 combo , if i put my th 350 tranny in any gear my engine stops after 10 seconds, it runs fine in P or N.
i don,t have a vacuum leak, i have a complete new 65000 hei ignition, and also a correct tuned new Holley 650 double-pumper
my fuel pressure is 7 / 8 psi
if i pull the vacuum hose from the vacuum of the hei nothing changes in rpm,s or engine sounds.
here in The Netherlands they don,t now it any more.

what could be the problem ?

regards Pat, The netherlands.