Jerry, we have a 3385RL and I pulled it for almost 2 years with a shortbed Ford so my answer to your first question would be no, you do not need a slider hitch. The GVWR (gross vehicle weight rating) on my 3385 is 14,000 lbs. The CGWR (combined gross weight rating)for my Ford was only 20,000 lbs. On my way to florida last year I had the truck and trailer weighed and the combined weight was 22,325. As you can see I was over weight by 2,325 lbs. Too much and I constantly worried about it. I now drive a Chevy 3500 diesel dually with a CGWR of over 26,000 lbs. Find out the GVWR for your 3455RL. I would think it's close to 14K. Also you need to know the 5th wheel tow rating for your F350. You didn't say what year it was. If it's newer than 2005 then your truck is probably capabily of handling the 3455. However, the most important number is the CGWR. You should be able to find this in your owners manuel, if not then the internet. Your truck is going to weigh between 7500 and 8000 lbs so the gross weight rating should exceed 22,000 lbs. This is not easy to understand so I hope I have made myself clear. I think you are probably ok but you need to be sure. You rest easier at night knowing you have enough truck for the job.
Larry Neal
2009 3385RL BH
2007 Chevy 3500 Duramax/Allison Dually