I'm also using feed tube D also. My set up is the same as yours and yes I read the directions. I read them twice before I started setting up.
Mine was set at 3/8" above the slide rail also as per the directions.
This is a pic of your set up from your last post and my set up from my first post. Look the same to me. Mine was also 3/8" from the slider rail.
As you stated the Pro 6000 has a longer rail so you have more room to work with.
I think what your missing is I have to work around this embossment sticking out that eats up some real estate on my shorter rail, real estate that you still have on the Pro 1000.
The Pro 6000 I think also has this hole but it has the longer rail.
When I first set it up I thought it was running correctly until I ran about 20 rounds through it in a row. Of course I was loading at that point, Then one would land on top of the gate with the ram up,
I was almost done when I found this problem caused me a double charge from fighting with this case feeder gate with the ram in the up position, and I had to go back through and tear down 100 rounds I had just loaded and I found 3 more double charges.
That 5 tube feeder isn't going back on the ABLP.
I did put the 5 tube back on the APP deluxe to try .327FM on it for priming, I took spring tension off the gate like you guys said and it is working fine on there.
What I thought was the case feeder gate holding back the case slider, ended up being the loop on the slider spring had enough play in it at it's attachment point on the press head, that the spring wasn't pulling the slider forward the whole way every time.
I had to shorten the loop on spring of the case slider to get it to pull the slider to the "stop" every time, so the cases lined up with the primer. That cured almost all of it but I'm not done with that problem yet.
I found out even without the case feeder I had to push the slider with my finger, the last 1/16 or 1/32" to get it to prime.
It's priming pretty well now and the 5 tube case feeder is working well there so there it will stay.