I have a 69 chevelle 250 inline 6. I have repleced the carb with a holly rebuilt. I have timed the engine set the points and set the idle. When I start it it will run good when I drive it and come to a stop it will want to die. I can catch it by hitting the gas quickly and the rpms will come back up. I have set the idle very high and it will still do it. Before I replaced the carb the engine would almost die but it stayed running with no help.
The car sat for a while and when it was restarted it had piston slap. I think that this may be part of it but I am not sure. we used slick 50 and that seemed to fix it. We also changed the oil. Also the tranny leaked all its fluid out over the time the car was stored. We have refilled the tranny and it does not seem to leak now.
If any one has any idea I would be greatful for any help.

Oh and it is only when coming to a stop in drive that the engine will kill. It will not do it in reverse. I also have the 2 speed powerglide.

I think you may be experiencing a fuel 'slosh' condition in which the fuel in the float bowl swings forward and into the bowl vent which then dumps a little gulp of fuel into the throttle bores causing the stumble.
If your 2V Holley is the one which resembles half of a double-pumper you can install a vent baffle. While you're looking for one that fits your carb just slide a 2 inch length of rubber hose over the vent tube that sticks straight up right next to the accelerator pump squirter. Be sure the hose fits tightly onto the tube.
You may also need to lower the float level about an eigth to a quarter of an inch.

Good luck,

Louie