Learn Spanish (Latin America): Incluso con el piñón nuevo, este desnivel es imposible. - Even with the new gear, this gradient is impossible.

Yes, absolutely. In affirmative statements like this one, incluso and hasta both mean 'even' and are completely interchangeable. You could say Hasta con el piñón nuevo... and it would carry the exact same meaning and tone.

I learned that aun also means 'even'. Could I use it here instead of incluso?

Yes, you could say Aun con el piñón nuevo..., but incluso and hasta are much more common in everyday spoken Spanish for expressing 'even'. Keep in mind that when it means 'even', aun is written without an accent mark. When written with an accent (aún), it translates to 'still' or 'yet'.

What exactly are a piñón and a desnivel in this context?

This sentence is almost certainly about cycling. A piñón is a sprocket, cog, or gear (specifically the rear gears on a bike), and desnivel refers to a gradient, slope, or difference in elevation. The speaker is saying that even with an easier gear installed, the hill is simply too steep to climb.

Why do we use es imposible instead of está imposible? Isn't the attempt to climb it a temporary event?