First, I would have save all documentation from your dealer visits and take them back to the dealer and tell them to make it right. If they refuse, find the number to the regional sales office and give them a call. If you had it in that many times and they couldn't find the problem, then it should be on them if it's still not running right.
Also, let's see if we can't diagnosed the problem. You say it runs find for about 30 minutes. Does it start to act up at a particular location on your property or just a flat 30 minutes. If it's at a certain place on your property if could be a faulty or overly sensitive seat switch. Engines just don't die without some cause, so the things you replaced, especially the fuel filter are the ones I would have replaced. How about a relay?
Talk to a small engines repair who has experience on Briggs engines and get his opinion also.
Also, let's see if we can't diagnosed the problem. You say it runs find for about 30 minutes. Does it start to act up at a particular location on your property or just a flat 30 minutes. If it's at a certain place on your property if could be a faulty or overly sensitive seat switch. Engines just don't die without some cause, so the things you replaced, especially the fuel filter are the ones I would have replaced. How about a relay?
Talk to a small engines repair who has experience on Briggs engines and get his opinion also.