2002 blinker light replaced works but sometimes

There should two separate bulbs for marker and blinker. It sounds like a bulb is burnt out, bad ground, melted socket or a wiring anomaly. Are you certain it's supposed to have 57 series dual element bulbs for blinker and markers?

Your right rear turn signal bulb is blown.Replace the bulb and the fast blinking will stop.

the blinker is bad, yes no kidding it is a relay type part. usually it is silver cylinder shape. When these burn out it will not blink. Easy to replace, just like a fuse, unplug the old one plug the new one in. Sometimes the part is called a flasher. Hope this helps

check all of the bulbs on that side 1 of them my not be working(it may light up but not flash because some of those bulbs are combo bulbs)meaning that some turn signals are used by part of your tail lights or break lights.

check the socket connections what ever bulb is not working is were the problem lies

You probably already know this, however the GMC 2002 Yukon Denali uses the Wagner 3157 (or equivalent) dual element bulb. The running light uses one element whereas the brake & blinker share the other element that burns brighter.

Check to ensure the correct bulbs are being used. Then check all wire harness connections. Since the blinkers function, then it sounds like the connections are good.

It really sounds like there is a bulb issue, so check that first, then let us know the results.

check the relay and blown out bulbs will cause the lights to blink fast or some to stay on. one bad bulb will cause the problems.

replace the drivers front bulb. There are 2 different elements in the bulb 1 for park lights 1 for directional

check your wiring harness to breaks and shorts also check to see if water is getting into the turn signal lense through a crack

If new bulbs don't work, it is probably the harness that holds the bulb. I had to replace both on my car after fighting with the problem for over a year and not knowing.