signal flashes fast on right side 99 yukon denali

1999 GMC Yukon Denali w/5.7
I failed this truck on an insurance inspection for no brake lights or signal lights, among a lot of other things. Approval was given to repair everything and diagnose the light problem. The fuse box under the hood was no pinned for anything brake related, although the cover said it was supposed to have a relay and a fuse there, which I found odd, but it wasn't pinned so I just moved on to the interior fuse box. The 20 amp mini fuse for the brakes/signals was blown so I figured I would replace it to see if the lights worked then try to figure out what caused it.
This truck has a lot of aftermarket stuff on it, alarm, stereo, winch, back up camera, GPS, etc, etc. After I put the fuse in the 4 ways were going, I had pushed the button previously and noted it had the typical sticking hazard switch which is common on the late 90s GM trucks. That was working fine, all 4 lights, 8 bulbs, 6 front 2 rear. Checked brake lights, worked fine. Left signal worked fine. Right signal flashes fast, but none of the bulbs are burned out. I did notice the right front headlamp and signal housing are new, compared to the left side. I haven't had the chance to take it apart yet and look at any wiring, as I was already working late.
I wanted to just ask if anyone else had any experience on this vintage GM with a similar lighting issue that may have popped the fuse. I done some reading but nothing seems to be on a GM. I read it could be a flasher or a ground, which I plan on checking. I know the tail light circuit boards were a problem on these trucks, have replaced a lot of them, but never for this, has anyone had this issue relating to one? Any insight on this is appreciated.

I was able to fix the issue of it flashing fast on the right, not sure if the fuse will pop again though, do to some interference from all that aftermarket stuff at some point. Check the circuit boards in the back, everything looked ok. Moved to the suspicious new right front signal housing. Both sockets were bent and severely rusted, and it looks like some one tried to clean them with sand paper. The wiring into both sockets was bare and shorting out to something, not sure power or ground. Replaced both sockets, reused the bulbs as they looked new, everything works like its supposed to.
I will add I did find that the small ground wires under the hood that go from the batteries to the body, were broken, all the battery connections which were all aftermarket and poorly done were all loose, and the connections to the mega fuse on the fan shroud were all loose. I was confused by the mega fuse, as it is the same that is on the 07 up GM trucks/suvs that's on the firewall or pos cable depending. I have never seen one on this vintage of truck, but the shroud is all reinforced behind it and with built in screw nuts, so I checked apparently it is OE on the Denali with a 140amp alternator setup. Either way all these problems combined or not, was causing my problem. Add in all the little extra stuff I had to go to the autowrecker for to fix stuff so certain problems won't be caused again.