I have a concord gas furnace when t stat calls the flame fires up then shuts down again this this tries this 3 to 4 times before it will stay ignited through cycle.this is a high efficiency gas furnace model rgu90a100d14-1b serial 8497g14263

Clean your flame sensor or replace.

I agree with the info you gave it sounds like the flame sensor is dirty. Turn the power off to the furnace and scrape it with a knife.(If you use sand paper to clean it the glue from the paper may stick to it making it worse than before)

I`ve found steel wool to work very well