340 camshaft question, yea another one.

Yeah Ima thinking the tune is off.
And whatever else you put into it, the tune will still be off.
And if that is so, then the new smaller cam will still be needing a tune.

Reading between the lines, it seems that your engine does not idle that well with the 274. Heck that is an easy tune. My 276/286/110 will pull down to 550 and pound pistons there as sweet as can be.
But if your TC is pumping oil, at your chosen idle speed, I can see a conflict right there. Mine's a stick,so I don't have that problem. Mine idles at 700/750 all day long.
I agree that HAVING to slip it in and out at every stoplight would get old for me in just one afternoon.

If it's not too late, we are here to help you put a tune into it.