I still have both! A '99 7.3L ordered in May 1998 as soon as they would take an order, driven only by me 91K miles. And now a new 2015 6.7L, driven only by me about 500 miles. They are identical except for year: F350 2WD DRW Lariat trim Supercab automatic long beds with camper and tow packages, 3.73 gears. Both have completely stock drivetrains. This as direct a comparison as you will get.
I haven't put the camper on the 6.7L yet, still futzing with wiring connectors and camper hold downs.
Exterior: so close my brother thought they were the same truck. Rear fenders are slightly different, as is the hood and grill.
Interior: new truck nicer in some ways. Seats are more comfortable. I like the climate controls, audio system, navigation system. Old one has a CD/cassette tape player (no 8 track :)). Switch gear is OK, not really improved. Drink holders are better. At highway speed, new one is MUCH quieter, can't hear the engine, can hear the radio!
Powertrain: the engine seems much more powerful and throttle response quicker. It will pull from just above idle in 6th gear and accelerate on grades that the 7.3L would be downshifting. I will know more when I get the camper on it. The transmission is both more controllable, and more intelligent, the large spacing to overdrive is gone. There is no long delay starting as the glow plugs heat in just a second or two. It has the same slow warm up though. Less vibration and very little clatter at idle. The 7.3L consistently got about 19-20 mpg empty on the freeway, and 14-15 with the camper. Only a couple of drives on the new truck empty, it reports 18.4 average since new and around 20 on freeway trips. I have seen only one regeneration cycle, during which I got 12.5 mpg for about 20 miles. I will need a few fillups to confirm the accuracy of the gages.
Smog controls: numerous on the new truck. A DEF tank, a particulate filter, a whole separate cooling system for the EGR. Most of the trouble that is being reported with these engines originates here. The electronics are very complex and obscure. Something as simple as circumventing the reverse camera lockout is nearly impossible, it is all done with serial network communication between the numerous modules. If you run out of DEF, it complains, then reduces power, and finally shuts down. EPA regulations. Open the hood and you cannot see the engine buried under all the stuff.
The ride empty seems about the same, but the new truck payload is about 2000 lbs greater.
I need to get the camper on it and see how that feels. The '99 has airbags, Rancho 9000 shocks, and large anti-sway bars front and rear. On this one I may not do the airbags.
So far not regretting the purchase, and the '99 will shortly be on Craigslist.
