it should be a lock nut too. i like to stake it in a couple spots also to keep it from ever backing out, and put a little torque seal on there for easy inspection.
When I come up short on info from Navistar I put in the DANA # and do a web search. My 2008's came with 19060S assemblies. Give that a Google "DANA 19060" and you'll get a PDF of the manual so you can get your specs.
M36-1.5 threads on a 19060S is 575-703 Lbs.-ft. YMMV...