Check or replace your fuel lines and filter first, then if it's still acting up, might be time for a replace/rebuild.
I just had issues with my 27 Kohler on my mini skid with 400 hours. Had replaced the filter last year, but had issues with running rough, starting hard and shutting down when hot.
Finally took it to the dealer and they replaced the filter and cleaned the fuel line, and since it's running great again. I'm blaming it on the stupid ethanol fuel.......
Did your mechanic do a compression test? If not, have him do that also. That would be my smoking gun for a re-build.