13 jets ?
that's not tuning.........that's an overhaul.
If you need to go that many jets in either direction , you have done something horribly wrong with your life.
Did it keep getting quicker with each change ?
I am no Holley guru by any stretch , but I do think a 408 would want more carb and I do think that more than 4 or 5 jets change means your baseline is off by a good bit or you have other issues at work.
I'd be looking for a friend with a bigger carb to try on there first.
But if there is a problem outside the carb like an air leak.......it won't matter what you put on there.