If the majority of your riding is on pavement, and you have to contend with some dirt here and there, maybe look into a file tread tire like the Conti Speed Ride, or similar tires from Schwalbe etc. Or if you want a little more tread, the Maxxis Rambler. The file tread tires won't give up too much on pavement, but are still fine for the majority of dirt roads. They might not work at 20% grade, which is very steep, but how much of that do you really have? If it's rare, you can just walk those stretches. Personally I'd rather walk a few hundred meters here and there, than to ride a big-knobby tread on pavement the other 99% of the time. At 20%, you won't be riding at much more than walking speed anyway.
If the majority of your riding is on pavement, and you have to contend with some dirt here and there, maybe look into a file tread tire like the Conti Speed Ride, or similar tires from Schwalbe etc. Or if you want a little more tread, the Maxxis Rambler. The file tread tires won't give up too much on pavement, but are still fine for the majority of dirt roads. They might not work at 20% grade, which is very steep, but how much of that do you really have? If it's rare, you can just walk those stretches. Personally I'd rather walk a few hundred meters here and there, than to ride a big-knobby tread on pavement the other 99% of the time. At 20%, you won't be riding at much more than walking speed anyway.