gmccall,
You want/need more than another year warranty- you want it fixed NOW, to work as intended, without further delay.
Don't settle for anything less and get the factory rep back on the line, and involved in the resolution process. Otherwise you could miss another mowing season with $8K invested in a piece of machinery you cannot use. Find out exactly what they plan to do to fix it and when. Be polite but stern, and follow up every conversation with email confirming your understanding of what they tell you, promise to you, like the warranty extension. Steady pressure kept on, no letting up.