The stock fan uses a temperature sensitive fluid to control the relative speed. It is possible it could be stuck on high speed which causes the roaring. Since the "clutch" is in the fan (a sealed unit), all you need is a new fan. If I had this problem, I'd just install an electric fan like the flexalite 183 for $350. If strapped for cash Im sure a stock fan could be found at a junkyard for $20.

 

The electric fan kits like the flex-a lite 183 and 180 come with a controller, so when you want the fan to kick on you set it to come on at a predetermined temperature , and then it will come on there always, so if you want it on at 180 degrees, it will kick on and reduce your temperature 15-20 degrees then turn off. Same thing at any temperature setting

 

Thanks for all the responses, I just decided to go the poor mans route and change the fan clutch for a used one from a 2007 Ram. It worked like a treat. Truck sounds so much quieter now, I can't believe the difference and I can't believe I've been driving it like that since I bought it about 18 months ago. I deserve a kick in the butt for that. On another note, it took about 15 minutes to change it over. I even made myself my own handy tool for the job, to hold the water pulley in place, so managed to save a few dollars as well. All in all about a $40 job.

Thanks again for the help and I hope this thread helps someone else out.