I have just bought a 2013 F-350 6.7 and dont seem to have engine braking . I have tryed to use Tow/haul mode to get it to work but notice no added braking or sound change .The truck has been empty when attempting so mabey thats why theres no diffrence ?

 

That's because there is none all tow haul will do is extend the shifts and downshift sooner. The only extra braking effort you'll get is the trans downshifting.