E-450 VS F-53 chassis, both have Triton V-10 but different "maximum towing capacity." Set aside for the moment the 20% difference in peak horsepower rating of the V-10 in F-53 and SD pickup VS E-series, because that increase in 2006 did not change the ratings on the F-53 from what it had been when the two platforms had nearly the same HP rating. Engines, and horsepower ratings, do not alone determine what can be towed. It is also not necessarily gearing. To further confuse things, look at Ford's ratings.
E-350 van with V-10 and 3.73 gears has GCWR of 15,000 pounds, tow capacity 8300-9100 pounds.
E-350 van with V-10 and 4.10 gears has GCWR of 18,500 pounds, tow capacity 10,000 pounds
E-350 cutaway or bare chassis with V-10 and 4.10 gears has GCWR of 18,500 tow cap 10,000
E-450 cutaway or bare chassis with V-10 and 4.56 gears has GCWR of 22,000 tow cap 10,000
For several years beyond 2006, F-53 with more powerful V-10 and 5.83 gears had GCWR of 26,000 pounds and tow capacity limited by only that, up to almost 12,000 pounds, but could be as little as 4000. Recently Ford has been rating the new heavier versions of the F-53 with a slightly higher GCWR on high GVWR models to ensure tow rating of at least 4000.
Something other than power, and even the GCWR, is limiting E-series tow capacity to 10,000. Where the GCWR is 18,500 and higher, there is almost 12,000 pounds difference between GCWR and the empty vehicle weight usually used to calculate tow ratings. In the case of the E-450 cutaway, that difference is almost 17,000 pounds, but of course somebody always builds something on that chassis that adds to the vehicle weight. What's limiting tow ratings on V-10 E-series could be frame strength, suspension, steering, or a "tail wagging the dog" issue. Actually, the E-450 was once popular as a commercial tow vehicle, with a lightweight utility body and heavy duty hitches, for loads up to about 15,000 pounds, until dually pickups started catching up with higher class 3 ratings.
So yor tow ratings from Jayco don't have much to do with Ford's ratings of the chassis (GCWR) nor does it go back to what engine or engine version. Build enough house on an E-450 to bring weight to 14,000 pounds, Ford's rating says it can still tow 8000. But in building a house, Jayco has done things to make them reduce the tow ratings: lengthened chassis to move the hitch further back, installed a lighter duty hitch receiver than Ford's Class IV or V, and used up most of the carrying capacity for tongue loads.
Same with the class A on F-53. If Jayco has built that one up to 18,000 pounds of house, using up most of the GVWR, there is still enough of the 26,000 to give it a 8000 tow rating, unless compromised by frame extensions, altered balance, or lightweight towing equipment.
Tom Test
Itasca Spirit 29B