#1
are you actually loosing oil? after major service the truck may smell of burning oil for a while...
#2
it could be ball joints, or pitman arm or something... it's definately realted to tires/allignement... should have taken it to Nissan for that. seems no one can do it right outside of them... check for wear... i'd check those and see if it may have been caused by the tire folks..
#3
belts. well, if they retightened them and they squick again soon then your belts are shot my friend.. probably have 105k miles on them... if they are Nissan belts then that's most likely... you can get all of them kellys for about 10-15 bucks..
#4
could be related to either service... it depends on timing...