3rd redo gearbox in 6months?

hey guys, new member here, got a 96 hilux with after market turbo, 30" muddies and 2" lift and empty tray, had the turbo installed at 180,000km and it went sweet till 285,000 till the gearbox gave up, so paid $1,500 for a reco box, then $700 for the install and it lasted 2 weeks of highway driving and went again, so got another one which was apparently completely rebuilt, brand new parts, and that one lasted 2 months until it went, they are claiming I over loaded it some how, I have 9 almonds in the tray, boost is still running at 8,000. What else could be going wrong? Is there an underlying isssue or am I getting fucked over? Had to pay again for the most recent box too, all been done through all 4x4 spares Australia.