I had a 4.3 5spd back when...
It was a great little tough truck, but if I had to do it over again, I'd get the 4.8. same mileage, better towing, and with a tune, even better than that.

 

I pulled a Uhaul from Florida to New Mexico with my 4.3/5 speed, about 2k miles total. The trailer itself weighed about 900 lbs, towing that by itself was nothing. I am guessing loaded down it was well over 3k lbs, maybe more. I just left the truck in 4th, towing about 2500 RPM at 65 mph, and it did okay, I was getting about 15 mpg.
Did I wish I had a v8? Absolutely. As mentioned before, uphill isn't the greatest, merges could get scary, passing Swift trucks could even be a chore. (some of you might get that.)

 

I understand that all too well I need to get a V8