cause for my onan gen to be 5500 marquise to be surgeing

Assuming you re-installed the governor mechanism correctly, surging on small engines is almost always due to a clogged idle jet/circuit. I know you said you replaced the carburetor, but dirt might have gotten into the new one.

Every time I change oil, in my 5500, I have to make sure that I do not fill to the top of the xxx on the stick. If I do it will surge and eventually stall. If I bring the oil to the middle of the stick it will smooth right out. I just have to check the oil level every time I use it, to make sure it is not running low.

You replaced the carb.. Surging is a sign of a fuel mixture issue.
Possible causes can be supply (Friend mentioned pump and filters also the fuel lines) but .. If by "Surging" you mean speeding up and slowing down Speeding up and slowing down ON a governed engine that indicates TOO RICH as I recall.

Missing = TOO LEAN

The carburetor adjustment instructions will point you both the the proper screw and which means which. Alas, List time I set a carb was around 1977 and some memories.. ... Well.. That's what 40 years ago.

Did it surge before you replaced the carb?

Did you change any of the linkage or spring settings? Was there a very thin spring that covers the linkage and hooks into the arms? On some engines that spring takes the slight slop out of the linkage and is important. If the fuel supply is good and the carb is new/good then you may have a gov issue. If you choke it slightly and it smooths out it may be a little lean. If the carb is new we would assume all is clear inside it yet a too low float level may affect it.

Could be carbonned up inside the engine. Most gensets do not get run enough under a good load to burn the carbon build up off.
There is some cleaners that can be sprayed through intake to remove some of it.
Gensets need to be run around 70% to get them hot enough to keep clean.

look under the unit is where they are at also did you set your altitude setting