Conclusion to Short Cycling
Gas Co. Tech measured draft in flue with old inducer blower and demonstrated how draft kept reducing; at first with inducer, then flame engaged then fan motor. It went below what I think was 4.5 (something like that with meter that looked like VOM). This kicked the pressure switch and shut down the flame.
He installed the new inducer motor and kept the old switch in place...inducer engaged, then flame, then blower....ALL OK...flame stays on just fine, no cycling...apparently inducer blower was bad. He replaced the pressure switch with the new one anyway and the unit operates fine. We examined heat exchager and firebox and all looked good. Flame was also consistent through all cycles.
Thanks to all for help...