I'm having the same problem so when the weather improves I will go up on the roof and force water into the vent pipes while a helper inside makes sure sinks are not putting out
I'm a little reluctant to use a snake because they can sometimes get stuck.
I had a kitchen clog so I forced water into the drain downstream of the disposal and then had chopped, fibrous food coming out on the roof.
The fix was to put one of these inflatable barrel-shaped pipe stoppers in the vent so the water had to clear the clog instead of going out the vent.
50 PSI at 6 GPM with hot water works pretty well. A 10' vertical vent pipe only gives me about 5 PSI of pressure.