this might help .
www.pirate4x4.com
LED fast blinker fix 81980-22070
just re adding this info. if you have this flasher this mod works by removing the lamp faiure circuit. BTW if you want add the resistor, then you will need a 6 ohm - 50 Watt resistor like this: http://superbrightleds.com/tail-brake-turn.html (bottom of page) It sounds like the 3rd gen trucks...