Are you using a Kohler brand fuel filter?
Kohler engines are well known for being extremely picky about their fuel filters.
Some "aftermarket" fuel filters are only made to "look like" the filter they are substituting for, and don't have the specified flow rate.
Personally, I buy a larger inline fuel filter at an auto parts house and I know I am getting sufficient flow rate.
You only need to know the hose diameter (usually 1/4") and choose a filter that IS NOT for a fuel injection system.
The reason fuel injection rated filters for cars should not be used is because you will pay 2X or 3X the price because of their heavier construction.
If you can put up a photo of your spark plugs so we can see the color (which is a reflection of combustion chamber activity) we may be able to see if this is caused by insufficient fuel (or not).

Yes I'm using an Exmark fuel filter. The fuel is not the problem, getting plenty fuel. Plugs look good.

Where is the SAM located, might be on to something. because it seems to me like a timing issue

Jim, check your e-mail. I sent you a service manual.

How much does a SAM cost roughly

How "fresh" is the fuel?
IF you have water/crud in the gas, it may be sitting on the bottom of the carb bowl until you speed up/load the engine. Then, the increased fuel flow may be enough to "stir up" the crud and allow it THROUGH the carb.

Fresh fuel, dumped and cleaned the tank before installing new carb

didja dbke-chk for the correct type of plugs? a "wrong" type could be breaking down under increased heat/load.... or try spraying some rattlecan carb cleaner around the the intakes and carb connections with engine running at "missing rpm" to spot an air leak....

Some of the DSAMs have been replaced with DSAI components. Without the spec, and a better description- there isn't a lot to go on. Could be the root of all evil.It seems to me the Exmark was the subject of current surges when the PTO engages - thus damaging the ignition components. This years and or last years service school notes.
Personally I think there also has been too much read into fuel filters and Kohler engines. I have never seen a model with a pump have issues. Pump filters can be the large canister 13 mic to 51 teardrops. Gravity feed systems can use the teardrop np if there is enough head, but need the small bodied ones (ideally a Kohler part) if not or if problems occur. Like was indicated above- equipment manufacturers don't always put the right stuff in the box! Though a twin has a pump...

No mention of changing the air filter, which this symptom sounds a lot like.
Mike

Typically, when a clogged air filter is the culprit, the chief complaints will be:
Heavy exhaust fumes smell and/or BLACK smoke out the muffler.
Spark plugs will be very black, sooty in appearance and may even appear wet or gummy, but the deep black color is the key.
Clogged air filters in themselves do not result in immediate symptoms involving "misfire" or "skipping a beat". But prolonged use of an engine with a clogged air filter can eventually cause misfire or even a dead cylinder due to the carbon (soot) deposits collecting on the spark plug. Eventually that carbon will develop into a conductor path that is easier to follow than jumping the open gap between the 2 electrodes. When that happens.........you don't got no more spark.