Koler Command 27hp

I have an older Snapper that has a 27hp Koler Command on it. I was mowing and the mower start to act like I picked up some trash in the fuel. I stopped and it smoothed out. It kept doing this so I switched tanks. It kept doing it and and then finally died. it will run with the chase on. I took it to the local shop and so far this is what they say they have done: drained the tanks, changed the fuel filter & pump, rebuilt the carburetor, put on 2 new carburetors, ran it on a known good tank & gas, changed the plugs, check the spark, changed the fuel lines, sprayed around the manifold while motor was running to check for leaks, check compression, did a cylinder leak down test. checked the valves, changed the lifters, and today they pulled the cam out and checked it with a mic (it was good). Everything has checked out good and it still will not run without the choke on. The mechanic now has an attitude and is saying that Koler is a piece of junk and I need to put a new Vanguard on it. This is still a strong motor and I see no need to spend the money on a new motor just because he can't figure out the problem.*
Any suggestions?

I am thinking that you have lost power to the fuel solenoid. On Kohler engines they will run with the choke on if the fuel solenoid isn't working. Possibly a wiring issue or maybe even a key switch issue. The dealer needs to make sure they are getting 12 v at the fuel solenoid.

Get a pair of bowl bolts to replace the solenoids on the carbs or blank off the holes if it has side mounted solenoids.
If it runs fine then the solenoids are the problem.
Cheap & easy test.
In future take the mower to a different shop that does not sell Vanguard engines.
Also , if the solenoids are the problem ask to have all your old parts replaced on the mower.
Or at the very worst ask for them back.
If the shop gives your grief, put all the old stuff on ebay / craigs list with an explanation that they are good but the workshop ( name them ) made you replace all of these good parts with new parts because they could not diagnose faulty solenoids.
Do not use any adjectives like incompetant, allow the reader to do that in their own minds