Could've been a cheap clutch. Beware of the puck clutch, they can be grabby as hell. The truck drivetrain wasn't up to making horses. A hydraulic clutch would've solved the flexing/cracking firewall problem with running a higher load pressure plate and the 5 speed will take scary power once it's fitted with a reinforced sump plate. We're lucky we have resources and info on building them nuke-proof on a real world budget. Poor Nissan and Yota guys have limited options I'll be curious to see how your trans install pans out. Least you know it's not as likely to limp off the road with busted teeth like it's been in a barfight...