Need some help figuring out why my rear dual case is popping out of gear. I have 2.28 in front with a 4.7 twin stick in the rear for an 86 4runner. The issue is the High/low shifter can not stay in low gear when going down hill. Even if i hold my hand on the shifter, it still pops out of gear so i just keep my foot on the brake. It's been an issue ever since I built the cases and installed it three years ago but not a big enough issue to worry about. However, it seems to be getting worse.
I've installed HD springs for all three decent balls (front and rear case), clearance looks good around the shifters, and the stock motor mounts look good. I've read that a lot of people have issues with the front case popping out when the shift rail isn't trimmed correctly but it doesn't matter position of the front case, it still pops out as I'm going down hill.
Would the shift forks be worn down on the low gear and it can't hold it position? Any help on possible solutions would be greatly appreciated.