My Bryant gas furnace (394GAD I think) starts up in heating cycle OK - but after a few minutes the blower shuts off. The burners stay on. Then 30 seconds or so later, the blower restarts. After a few minutes, it shuts off again - burners still on - then starts again after 30 seconds. Repeats this cycle until thermostat is satisfied. Any ideas?

Sounds like you have a fan/limit control that activates the blower. Depends on how cold your return air temp is of how often it cycles. The switch can go weak and short cycle but if it stays on after the house heats up I would say its working the way it should. Shuting the blower off -not to blow cold air.