BW-4410 help needed!

[rickpilgrim]

So today we replaced another BW4410 T case in ou 98 5.7 powered K3500 crew cab/long box srw truck. It spends 95% of it's time on the hwy and normally has an 8600lb trailer hooked to it. We use 4hi in winter 50% of the time, and 4lo is not used much.
At 156K mi today was the 3rd time we have done this.The first was under warranty@41K, Next time at 78K, then 121K and now at 156K. This time we got a BW 4470 for a diesel truck, looks the same but is supposed to be more HD. We get our rebuilt units from NAPA,just under a grand with a 1yr/12K mi warranty.
What you usually hear before it fails is when you let off the throttle on the hwy or downhill a screeching almost like gears stripping. You hear that 5-6 times and then a BANG and HI range is all gone, all you have left is 4lo.
We do the 12K mi fluid change on all, and untill they break the oil analysis is ok, and then the fluid looks like metallic pink paint. The cores are worth $350 so we have never taken one apart.The shift linkage is adjusted correctly and feels solid, no slop,no big tires, stock ride hight, shafts and U-joints balance ok and are good. Something here doesn't seem right, none of our other trucks have this problem, and they all tow this heavy or more but this is the only one with the BW4410.
Is this just a weak t-case and in need of a 205(more work than I'd like) or am I missing something here ?

[msgross]

ttt