The F150 first used EFI on the '85 5.0L engines.  The 300
six became EFI in 1987.  The 5.8L V8 was not EFI until
later.  The Ford F series always used port injection.  It
was switched from batch firing to SEFI as the years went by
depending on the power train config.  The 300 six will
handle a 3000# tow easily as long as you ar in no hurry when
accelerating.  It has better bottom end torque than the 5.0L
but, the 5.0L catches up pretty quick and holds it further
up the rpm range.  I have had both over the years.  I find
the 5.0L more to my liking because of it's better
acceleration in the mid range.  The 5.0L also get the same
or better fuel mileage.  Both have outstanding reliability
in my experience.  Either will handle your compact tractor
easily.  I highly recommend a trailer with brakes and a good
adjustable controller if you don't already have that.

My current 5.0L has 207k miles on it.  It uses aboput a
quart of oil between 5k changes, has good even compression,
the timing chain is still tight (I checked it a few months
ago when I had to replace the oil pan gasket which is a
common failure in '90's Ford engines) and it still maintains
60 psi oil pressure hot and idleing with 10w30 Havoline in
it.   The trans has been down twice - once for converter
shudder which is common in the early E4OD and again to
replace the front seal when I had it out to replace the oil
pan gasket and rear seal in the engine.  

IMHO, if you need a reliable work truck, Ford is as good as
any out there over the long haul.  I can say this after
having had the Toyotas, Nissans, C****'s and a couple of
Dodges over the years.

Lugnut