I have never seen anyone with even with a 26' Billfisher towing with a Weight Distributing Hitch; your GCVW rating of 20,000# would allow you to tow your 23 and still be under the limit; according to your specs the van weighs in around 6000#. You just can't drive around like you're in a race car; just be slow and deliberate where you are going. The 7.3 will pull it, if its a turbo even beter. You really need to make sure the Master Cylinder on the trailer is functioning and your brakes on the trailer are in tip top shape. Nothing however could improve your towing experience with this boat and trailer than a set of dual rear wheels, it really takes the sway out of the equation IMHO.