Well Cara, after reading through these two pages of posts, I can't think of any idea that has been left out. In my experience, fuel and ignition problems present with very similar symptoms. This makes it hard for us to figure out the exact problem. So I would do a test to try to determine if the problem is fuel or ignition.
It sounds like the problem is persistent and that you can observe the poor running by just opening the throttle under a load. The test is simple- Remove the cowling so that you can see the intake of the carb. Put some of your fuel mix into a small spray bottle. Run the engine so that it starts to die and then spray a short burst into the carb. If the engine continues to die then the problem is likely to be ignition. If it recovers and runs strong for a few seconds, then the problem is likely to be fuel.
Once you have the problem diagnosed to either ignition or fuel then you can concentrate on the answer.
I suspect that you will find that the problem is fuel-related. After you spent $300 for a mechanic to rebuild the carb and it still ran poorly, did you return and tell him that his repair was not effective? What response did he have?
Regarding the use of E0 gas, my experience is that all of my small engines (outboard, string trimmer, blower, chainsaw) are happy to run on this fuel with no problems. I have no experience with TruGas which also has no ethanol. So my opinion is that if it runs badly on E0, it will probably run badly on TruGas. But YMMV.
If the problem turns out to be ignition, a possible cause that hasn't been mentioned is a bad ignition module. These small engines often have a ignition module that fires the coil but also adjusts the spark advance depending upon engine speed. A faulty module that does not advance the spark will also cause the symptom you describe. But I still put my money on fuel being the culprit.