Enclosed trailer question

my dad pulled a 24 foot enclosed trailer with a very heavy load of goods with a ford econoline 250 with a 4.6 for like a month driving around 2,000 miles a week...it worked that little motor hard up mountains but it got the job done till he could get a 2008 ram 2500 with the 6.7...now he can fly up the mountains like he's in a sedan