By removing the air intake hose and having the set come up to speed, it is indicative of a blocked airway.
Just because the air filter looks clean, does not mean that it is. The filters are designed to trap very minute particulates, ones that can not be seen with the naked eye.
I would suggest first checking the air inlet hoses for kinks/blockage.
Then replace the air filter.
Do not try to clean these filters - always replace them.
The generator has on about 6 hours of run time and the filter is clean, it runs the same even with the filter out.
If it runs the same with or without the air filter in place, the hose will have nothing to do with it.
UNLESS, the governor, throttle, or choke linkages are rubbing against the air hose.
If this unit only has 6 hours on it, it is a new unit and should still be under warranty (unless it was sitting unused for many years).
If under warranty, you are much better off letting Generac handle it, so you don't risk voiding your warranty.