Are you serious? I have over 900 ft lbs on mine..the NV5600 is rated MAX at 650 lbs ft of torque, what's your truck make max?
800 lbs ft will walk right through 6th gear and set it up for failure
do you tow heavy?
what tranny lube and how much?
any PTO cover coolers on the tranny?
stock NV5600s run too hot towing heavy