New tow vehicle/old hitch.. What to do?

You're in the same predicament I'm in. We recently ordered a Jayco 28RLS TT to replace our 5th wheel. Your trailers tongue weight is advertised at 625 lbs. Mine is 700 lbs. Add propane and a battery and all our junk in the basement storage and we're likely over 800 lbs tongue weight. I hitched up to a 28RLS on the lot and the truck only squatted 2" in the rear and the front didn't rise at all. With the salesman, wife and myself standing on the tongue, it dropped another 1/4"~. If not for the capacity rating of the receiver at 600 lbs, I'd much rather use my short draw bar ball mount with no WD. But to satisfy the receiver's rating, I ordered a Reese trunion style WDH with 800 lb bars. I wish we could still get the ol' Quality S WDH with the very short welded ball mount. I realize the length of the hitch is for vertical leverage with WD but it also gives lateral leverage that adds to push with those passing trucks. I've even considered drilling another 5/8" hole in the Reese 54970 shank to shorten it up as I want less distance between the ball and rear axle, not more.