Recently rebuilt the 304 in my ute. It's a VP efi, with a bit of a cam and matching chip. All back together and have done a few miles, slowly sorting out some issues. Timing to +12, New plugs and gave the IAC valve a good clean, so now I good smooth idle, and decent acceleration, but if I just poke along, especially lowish revs, it's got a hesitation or stumble. No fault codes are coming up, and it seems to be there warm or cold.

No pinking under load, so could handle a little more advance, but that wouldn't be causing this issue, or would it?

Any ideas?