Gasser will be better for short trips, or don't care about towing power/efficiency. With that 25 mile trip it shouldn't be too bad, I drive 35 miles each way. Definitely let her warm up, with proper maintenance the 6.0L is a great engine, the 7.3L can be neglected. So if you are anal about maintenance, get a 6.0L, if you sluff it off, go with a 7.3L. I love my 6.0L, and I loved my bronco with 351W but i hated that when I towed anything i got about 7ish mpg.