Can I get a vacuum lines diagram?

There isn't much to it. The second drawing is for the evaporative emissions system.

How long since it's had a tune-up? Better suspects would be old spark plugs, and possibly an EGR valve stuck open due to a chip of carbon getting stuck in it. GM engines are very picky about correct fuel pressure. Some won't even start if pressure is just five pounds low. You might consider attaching a fuel pressure gauge and running the hose under the rear of the hood to a wiper arm so you can watch it when the problem occurs.

Have you checked for diagnostic fault codes or just relied on the absence of the Check Engine light? If you don't have a scanner or code reader, the people at most auto parts stores will read them for free. Be sure to write down any code numbers, not just the descriptions they give you.

So there's no misunderstanding, there can be diagnostic fault codes set even though the Check Engine light is not on. Well over 2,000 codes can be set. Only about half of them refer to things that could adversely affect emissions. Those are the codes that turn the Check Engine light on.

Given there is a misfire and the warning light is not on, it is likely the cause is not spark related, or it doesn't last long enough for the code to set. Single-cylinder misfire codes, for example, need to count the number of misfires before the code sets. For that, you'd get code "P302" if it involved cylinder # 2. For that, we'd look for something that only affects one cylinder, like an ignition coil, spark plug, or burned valve. Very often those misfires can't be felt, but the computer can detect them.

If you get multiple single cylinder misfires, or "P300", random cylinder misfires, we'd look for what they have in common, like the low fuel pressure. A chip of carbon can hold the EGR valve open. That valve must never open at idle because you will feel it. Since the computer isn't commanding that valve to open at idle, it's going to command the correct amount of fuel, but there won't be sufficient fresh air to go with it. You'll have low idle speed along with a rich condition in the exhaust. That would show up on a scanner, but you'd need a specialist experienced in emissions system problems to interpret the numbers.

This could also just be a low idle speed problem from the way you described it. The scanner will display the desired idle speed and the actual idle speed. In the case of older Chrysler products, that is very common right after the battery was disconnected. It has a very easy solution, but until that is done, the Engine Computer doesn't know when it has to be in control of idle speed. Chrysler and GM used to use the same idle speed system, but they handled the software end of it differently. The fact the rough idle clears up by raising engine speed suggests the things you've done, and the things I've suggested are likely not the cause. Besides the rough idle, can you tell if it's idling too low? How long will it do that if you don't raise engine speed?

The description sounds like it's running lean from unmetered air. Low speed = higher vacuum and more chance of a small leak causing problems. As you open the throttle the leak no longer is an issue because it blends in with the throttle. You say you smoke tested the vacuum lines. Did that include the brake booster? No hard starting after it was filled with fuel? Do you have a scan tool that can read live fuel trims? If so, put that on it and look at the short-term trims at idle when it's acting up. Is it trying to add fuel? What do they do when you open the throttle?

Smoke likely went into it but it may not have leaked in an area where it was easy to see.
Okay, try this test: Find a parking lot that is empty or a road that you can stop on without power brake assist. Now disconnect the booster and plug the line from the engine. Now drive and see if it still does it when you brake. If it's stopped, you know the booster is leaking vacuum.