Are you, by any chance, started printing with no MG filters (contrast filters) then started using them for later prints? While no filter will produce the same result as grade 2 filter, the exposure time will be like 1/3 of the time.

Using 75 watts light bulbs in the enlarger, at f/8, typical exposure times for 8x10 prints are 10 to 20 seconds for most negatives.