Any diesel engine is expensive to fix doesn't matter which brand. I never did like the idea of aluminum heads on a diesel like the duramax has they seem to work but
Chevy trucks can be a maintenance pig when it comes to the front suspension sure the A arm system rides nice but your dealing with a h*ll of alot more moving parts. The older Fords even the newer Fords like the 05 and newer are simple aswell.
Chevs you have 8 A arm bushings you have 4 ball joints and something like 5 tie rod ends all waiting to cost you big money.
I prefer Fords myself its all I will own because the trucks themselves are better built and for myself the Ford dealer is the best to deal with when you need OEM parts.
I own a 6.0 I also prefer the 6.0 over the 7.3 I have had a 7.3 yes it was a decent engine but its no where near the power a 6.0 has. I have had good luck with my 03 6.0 I bought a 06 6.0 and its been good so far.
Where I live and what your putting your truck through everyday a 7.3 PSD life span is MAX 350,000 kms (218,000 miles) anything after that be lucky your not into a engine rebuild. There are a few around with 400,000kms (249,000 miles) but like I said a few.
The 6.5 diesels around here usually have a lifespan of 250,000kms (156,000 miles) and 5.9 Cummins 12 valves last about the same as a 7.3 PSD your not going to get much more than 400,000 kilometers out of a 12 valve.
So anyhow yes the 7.3 is good just make sure you buy a truck has has been looked after and the oil changed at the right intervals.