did you have your defroster on when they were slow?
my car if im at a light with the defrost on everything dims and blinkers go slow. alt and batt test good, connections cleaned, still does it. i just dont use defrost unless im moving.
mine do that due to my underdrive pulleys...i watch my factory volt gauge just go way down, and thus my blinkers slow greatly. I just put in an Optima red-top, but i think the alternator is payin the price.