Have natural gas hot air furnace with honeywell smart valve SV9520H8067. Unit calls for heat and ignites OK but only stays lit for 5 seconds and goes out. Have had smart valve replaced 5 years ago. Does this sound like another smart valve problem?

Every Smart Valve is a problem. The symptoms you described could likely be a dirty flame sensor. Normally I would suggest pulling it and cleaning it but with a Smart Valve it can be VERY easy to damage the igniter. If that happens then you are SOL.