Actually I know a number of people with over 150,000 on their diesel.
Need to decide if you really need diesel. If you just want one, ok but they don't pull even on cost until 115,000 or so. I've seen the studies since I just bought an 07 Dodge Cummins 5.9.
I had a Nissan Titan and that sucker seriously pulled a double trailer set up. 27' Coachman with 100 gallons of water in it, an ATV behind that and 2 dirt bikes in the back of the truck.
Pulled that rig from Pagosa Springs over two 10,000 passes to Silverton Colorado a number of times. Never missed a beat. Was overloaded on the payload by about 200# or so. But was fine on the tow rating.
The ricey rocked and hauled butt. Had almost 100,000 miles. It got 15-17mpg pretty much. Got 10 mpg average pulling heavy and my enclosed snowmobile trailer.
I bought a Yamaha Rhino that weighed twice the ATV weight and decided we wanted more juice and weight pulling the rig and snowmobiles. AND the big one is I want to stop using the truck for every day use in a year or two and keep it for an RV. We also may buy a new heavier trailer in the next 2 years. So we went diesel.
Ford is out of the picture for me right now. My son and my best friend have/had the 6.0 and disaster. My other son has a 7.3 and it is awesome.
So since I have some friends who I ride and RV with that have Dodge and they have had excellent luck with the newer models (05-06) I decided to try it. I get 19-20 mpg combined right now with 7000 miles on it. I get 21-22 on open road if I stay under 70mph. I get 20-21 at 75 mph.
If you aren't pulling major heavy and aren't going to keep your truck over 100,000 miles+++... look at gas engine in 3/4HD unit. I had a 454 just like you and got rid of it for the Titan just because of the gas issue (plus it was a dually and the tire rotation etc was a killer) Most of the gas engine HD's have higher tow rating since the engines are lighter. HOwever the tow ratings for diesel are listed low for tax reasons.
I really like the Dodge. Never had one before, was always a GMC guy. Duramax is king, but with Dodges's cost and our heavy off-road use I opted for Dodge this go-around. I also got the 07 5.9 with just the 4 speed auto. Tried and proven and I don't need the mega power of the new model. Good price also but not enough diff to buy the 5.9 vs the new engine/trans. I think the trans is much better in 07 and they used the junker 5 speed for a short time. I have an extended warantee so the trans is cover a quite a while.
Good luck... I hate buying vehicles.