Ok I have a 99 ford f250 manufactured 5/99 7.3 xlt 4x4

replaced the pitman arm but cannot get it to stay tight

I read somewhere they take a 170 ft pounds of torque

example I cannot even tighten it anymore, but even if I drive for 20 miles and jump under the truck I can turn the nut again

 

pry bar with a 3 foot pipe... and "RED" loc-tite.

or drive it to a local repair garage.. a 1/2 inch air powered impact wrench.. mine is 600 foot pounds.

 

X2 - go gorilla on it.