I also agree... . that mileage is just too low for the work your doing... .
Go thru your "air" system and look real close at all the fittings, hoses etc. Actually take them off the truck and look at them closely. With the rubber fittings, pull them off and roll them in between your fingers looking for "dry cracking" like old tires can show.
If possible, pressurize the IC and listen/look for leaks.
Next run a good healthy double dose of additive thru the pump. Use something that has more "focus" on detergent properties.
In my case the signs of flexplate failure started out sounding like a small rock in a tire... . after a few K's it sounded more like a metal screw in the tire... . a few more K's and it sounded like bad engine knock and finally it rattled so bad I knew it was the fexplate. Remember, if it bags out on you, chances are you won't be able to start the truck and will need a tow.
bob.....