Outhole coil? Don't you mean the autoplunger in the shooter lane?

Did you test the outhole (center ball drain), trough, and the shooter lane switches in the switch test using a ball or finger? If you use your finger, you may not notice that a switch may not be registering until well below the surface of the playfield or trough. Check them with a ball at least 10 times each. If you can't get them all to register all times, you need to adjust the switch(es).

I was blaming the software too when my machine thought I lost all balls when there was still one remaining after multiball. I ended up replacing the trough switch because it was bouncing.

You should install the version 5 ROMs if not done already. It did not fix that problem, but it did fix a bunch of other bugs I had.

This is what I am asking about. You actually meant autoplunger?

Just double checking...you're using a ball to test all the outhole, trough and shooter lane switches in test mode?

What version ROM do you have now?

Pinball Resource is normally the source for all things Gottieb. Though, Marco is starting to carry some parts.

The ROM version is listed on the first screen when you boot the machine. Mine says 742/5 with GPROM Checksum 89AA.
There are 5 ROMs and they are not all at the same version. Chances are you will only have to change the GPROM.
arom1.bin
drom1.bin
dsprom3.bin
gprom5.bin
yrom1.bin

There is a sticker showing you the ROM locations on the boards, look for it in the lower left corner of the back metal plate in the head. There should be a sticker on the ROM chip itself telling you its version.

The copyright owner enforces his copyright on these ROMs. That does not help much if they run out of stock.

Have you ever played virtual pinball like pinmame? It is as if you are playing on a real machine.

Don't expect this will solve your problem though. For me, it helped fix some screen display issues especially when scrolling.

The only ROM you need is the GPROM.
The copyright holder is pbresource but I did not see the Stargate ROMs listed on their site. You can try contacting them.
Another option is to find the file and get it burned on your chip.

Stargate is available as a virtual pinball. I am sure you will find it interesting.