are any of the rockers NOT spitting any oil, or very little oil at the upper tabs?
the oil travels thru the lifter, up thru the pushrod, then squirts thru a hole under those tabs.
that may help isolate which assembly is ticking.
you can also put the stethoscope probe directly on the bolt...
your Ranger cannot be "programmed" for flat towing.
for Ford's recommended procedure go to the top of this page and select tech library, then 1983-2011 Ford Ranger tech, go down less than 1 page and
select owners manual, select 2003, scroll down to page 148.
your 2003 does not like to be flat...