First Ford does not build a 3500HD so I assume you mean the F350 listed in your profile. 
Have you had the truck for a few years? Do you know the history of this engine? Does your concern rise only from what you have read on the internet?
I'd look at this one of two ways. 
1- Peace of mind, you just go buy a new truck. Most people will tell you to do this.
2- Your truck runs fine and you like it, but the stories concern you. If you know the history and the engine as run fine now, I'd keep the truck and be extra vigilant in my maintenance. Ford/Navistar made around 800,000 of these engines. Yes, they had a higher than normal failure rate (Ford bought back around 500 of these trucks), but there are still hundreds of thousands of these engine still on the road. Not every engine was bad.
I have a mechanic who specializes in pickup "light duty" truck diesel engines. He's certified from auto to class 8 diesel engine but likes working on the pickup truck diesel engine. You can probably find someone similar in your area and have him take a look and make a recommendation.