Outer Limits 4x4 Board

My high Low transfer box is cliking when in 4 low in 2nd gear while under power.
i beleave it is the chain slipping. This is the second time that i have had to fix this. Last time i had to replace the hole unit.

Is there any way in helping to stop this problem i have or am i just to hard on the truck.
the truck is 91 SWB soft top 2.5d

I'm guessing it's a super select t/case ??
If so they had much beefier chains than the earlier (non super select cases) and are reasonably strong.
Unfortunately there is no scope for adjustment and once they stretch have to be replaced with a new item ($500-600 from Mitsu).
Proby cheaper to get a 2nd hand t/case from a wreckers and keep your old one for spares.