Excels tend to be heavy and you will more than likely be over the trucks GVWR with a single rear wheel truck. A typical 5er will have a pin weight of around 20% of the trailers GVWR. Your Excel will probably have a GVWr of around 15,000# so your pin weight could be around 3000#.
A truck in travel form, loaded, full fuel and hitch will be considerably over the curb weight, so you need an actual truck weight.
Towing a 5er is limited by tow weights...the trucks GVWR and GCWR.
GVWR is stamped on the tag on the drivers door jamb. GCWR is in the owners manual and specific to an engine, type cab and axle ratio.
GVWR - loaded truck = max loaded trailer pin weight.
GCWR - loaded truck = max loaded trailer weight.
The weight tag also list the front and rear GAWR. The manufacturers literature will tel you that NONE of the weight ratings are to be exceeded. Some people feel it is OK to max out the rear axle and be well over the trucks GVWR. I do not.
Here is an excellent site to explain the terms and has a spread sheet to help with the calculations.
RV and Tow Vehicle Weights
The main thing is to know your weight limits and see what your comfort level is for your rig. You will get a lot of folks telling you that they pull their 40' 5er with a 3/4 ton truck and do just fine....they have no idea of their weights and are an accidenet waiting to happen.
Get the right truck to do the duty....ie. don't expect a boy to do a mans job.
In short, I think you will be better served and a more comfortable with a dual rear wheel truck. Watch certain years of the Duramax as it had some injector problems. Ford had a disaster with the 6.0L starting in 2003.