My work truck is a 2005 GMC W5500. I bought it used. It had 3 different rear tail lights. I went to the local truck stop & got 4 new matching LED lights. Now my turn signals blink too fast. Since the lights are built into a liftgate, there really isn't room to add the resistors. I'm looking to find a 3 prong LED flasher. Does anyone have any ideas as to where I can find one?

Napa EL13H
Signal-stat 263 or 537A