my suggestions would be
buy a can of SEA FOAM at your auto parts store, pour 1/2 of it in your gas tank, start your engine, pull the large vacuum hose off of the big brake booster canister, pour the rest of the fluid into that hose leading to the engine, read the instructions on the can, pour it slowly enough that the engine does not die. Your tailpipes are going to smoke for awhile
,,, i would never put it in the crankcase, even if i was going to change oil soon
change the spark plugs if you have not done them in over 40,000 miles
take the air cleaner filter out, vacuum anything that may be under the filter, replace the filter & reassemble everything.
air up your tires
change oil & filter
I just returned from a cross country round trip, over 6,800 miles & i have 83,700 miles on it. My MPG was pretty good considering the weight that i had in the Ram