As a 20 year Ford parts man & former 7.3L PS owner I can share some experiences.
If you are going to go diesel the 7.3 is the way to go. We recently started a diesel shop at a Lincoln-Mercury dealership just to take advantage of all the work on the later 6.0L & 6.4L that is being done. Business has been GOOD! I see nowhere near the problems on the 7.3L that I see on the newer Ford PSD trucks. The 7.3 PSD package is about as good as it gets.

As far as upkeep & operating costs 5.4 gas vs. 7.3 diesel.... Rule of thumb is higher upkeep on the diesel but more power, better fuel mileage {significant} & longer hard working service life from the diesel. The 7.3L & 5.4L both share the same E4OD/4R100 transmission & obviously are wrapped in the same Ford truck

. In an F350 the running gear & brakes should be very close to the same as long as both are the heavy GVW truck.
Personally I had a super cherry '95 F250 PSD that got great fuel mileage & was a pure joy to drive but I never worked it. Sold it, bought a Ranger & pocketed the cash difference. I miss the PSD, damn thing got nearly the SAME fuel mileage as the 3.0L Ranger does!

Overall, I would say go with a diesel, as long as it's a 7.3!

My sweet F250 PSD. Only had 85,000 miles. Now resides in Texas.
The replacement Ranger. Fits the needs but.........