Cyclone 4250 with Onan 5500 Generator

I am running generator. I turn on AC in either the den or master bedroom and then turn on garage, the ACs usually run fine. If the garage is already on and I turn on either the den or the bedroom, the generator circuits trip, and try to reset, but will not until I turn off the den or master bed AC. Another scenerio is the one of the two circuits will blow on the generator causing me to go to the generator and resetting the circuit. Getting very frustrating. Any ideas what the problem may be? Thank you in advance for your wisdom.
Hank Miller