350 Timing Troubles/Questions

[5Tractorguy]

With any luck someone here will be able to help lick this problem...

I'm having timing trouble again with my '88 V30 square. Engine is a 350 with a TBI and ECM from a '91 3/4-ton Cheyenne.

When I changed the EMC and TBI a year or so ago, I set the timing to 4deg. Should be running stronger, but better than how it ran at 0deg.

Serviced the truck a few days ago (including cap, rotor, O2 sensor, plugs...) and it ran worse. Checked the timing and it was up at 12deg, brought it back to about 4deg. Ran better, but when going up a hill it gets to a certain point where no matter how much you push the gas, there's no increase in power. Brought it down to 0deg, same deal.

Went on a small road trip to pick up tractors in NH today, ran with the same symptoms, power just wasn't there.
Got back home, brought the timing back to 4deg. Have yet to drive it again.

When I set it back to 4deg and plug the wire back in, the timing mark moves about 1" past the degree indicator. And watching it with the light, it stays in that exact spot from idle to high throttle. If you goose the throttle it will waver quick and them return to that spot 1" past the indicator.
Is the mark supposed to move as the throttle increases (as I assume a vac advance distributor would do)? Or does it move per the ECM only when the engine is under load?

I've posted here before about this issue and have been chasing it ever since the truck went on the road in 2011 after restoration. Its never been consistent on running properly, always runs boggy. Sometimes you'll have a good day and it'll run strong, but it always goes back to this. Just wish I knew what the heck was wrong