I have an immaculate Benz, 141000 miles, not scratched, dents, door dings, rips, cracks,etc. Runs great till near empty then its.......laggy...? Best I can put it anyways. Suction at the gas cap, runs great full.
That's not where this was going but I just remembered it.

What I was getting at is, yesterday on the interstate, drives as expected. I go to pass a truck, ever so slight puff of smoke, downshift, engine sounds like its working harder, but I'm not goin faster. That just dosnt feel right to me.

Now I know about the rod issues, but I seriously doubt I'm gonna be dealing with that for some years. You think the same if u saw this car. But something Is clearly wrong. I have watched the oil and it dosnt consume oil.

Suction at the gas cap is bad. Thats your fuel tank imploding. You vent line is collapsed.

How do I fix such a thing

Get a new vent line. I guess. Find the manual for your car it should be covered.

Or clean it. Its usually just caked with road grime.

That might be what I try first, money and all.