Engine replacement for 1999 Dodge Ram 1500, 5.9l Magnum

[NewToDodge96]

Bought my first Dodge truck about 6 months ago. A 1999 1500, with a 5.9l Magnum engine. The engine is nearing or over the 300,000 km mark (not sure as the odometer works only occasionally, due to what i assume is a transmission speed sensor, given that the speedometer also works only occasionally). I'm considering buying a new engine for it, but don't know where to look. The wife thinks its not worth it, but I do love this truck. I want to keep it to tow my trailer and use as an offroad/mud truck. So my question is, where should I look for a new engine? Any other advice regarding the 1999 magnums is also appreciated.

 

[Halligan]

Is the truck running poorly with the current engine? You could order a remanufactured engine from a company like Jasper and drop it in. What kind of condition is the rest of the truck in?

 

[NewToDodge96]

She idles rough when cold starting. There is a bit of a hiss sometimes, which I think has something to do with an O2 sensor. Burns really rich. Doesn't have as much power as I think it should. Really have to lay into it to break traction (and sometimes wont break traction at all) and doesn't much like pulling things. I've noticed a big change in gas mileage since I first bought it. Almost 20 litres for 80km now, not hauling.
As for the rest of the truck, putting into drive or reverse there is a but of a clunk sometimes, and of course it has front end suspension issues (Which I'm told is par for the course with Dodge trucks)
Body is in good condition (plenty of BC Pinstriping from backroads) Frame is good.

Ultimately I'm not getting as much power as I think I should from this engine, and to my (admittedly limited) mechanical knowledge, I do believe that the engine needs work at least, and possibly a replacement

 

[NewToDodge96]

Would a rebuild be cheaper than a replacement? Or for a truck of this age, should I look at replacing the truck? Though I do love this truck and would like to keep it. I don't really like newer vehicles. Too hard to work on at home I find. Everything is computers