Sorry to hear you're not making sawdust. Long bed jointers are prone to saggy tables, often from wear and gib adjustments. Since you loosened the gibs, and your jointer relatively new, I'd adjust the gibs. Start with the outfeed table. Use a jack and a piece of 2 x 4 and apply pressure/support on the outboard end of the outfeed table. Loosen the locknuts, and back off the gib screws until you feel no tension on the screws. At this point you should be able to turn them by hand if you wanted. Now give the jack a pump, lifting the base just slightly off the floor. Now just snug the gib closest to the cutter head, and while holding the gib screw with your wrench tighten the locknut insuring that the gib screw doesn't turn. Relax the pressure and snug the middle and bottom screw. Pull out the jack, double check and lock the middle screw, and finally the bottom screw. Next, lower the OUTFEED table 1/2 - 1 turn. If the hand wheel is a slightly difficult to turn that is okay, because once set the table is locked and never moved. Do not loosen the top gib because the table will droop. Repeat for the infeed table, but the gibs need to start snug and backed off ever so slightly if needed to allow the hand wheel to turn with just a little friction as it did when you got it. Resist loosening the top gib screw too much or the table will droop.
Now to dial in the jointer, find a 3 - 4 foot long board and set your infeed table to make about a 1/32 - 1/16 inch cut. Place the straightest edge, or slightly concave edge on the infeed table, start the jointer, then proceed to cut. Stop feeding the board once 1 - 2 inches are over the outfeed table. Shut the jointer off. Now slowly raise the out feed table until the table is almost touching the cut end of the stock while sliding it over the cutterhead and watching as the end of the board starts onto the outfeed table. At this point I'd be looking for less than a sheet of paper clearance. Now make a full pass, or 2. The edge should be very nearly straight. If it is, great. In all likelihood you'll have a very small snipe at the end as the board drops off the end of the infeed table to the very slightly lower outfeed. Now hold the edge of the board on top of the clean outfeed table. Get at eye level and you should be able to see if the edge sits perfectly flat on the table. Run a second board and mate them to see how they fit. Any errors will be doubled.
Finally, if it's perfect, you're done. In all likelihood you'll see a small snipe at the end thus showing a gap. That is what I was going for, as your last adjustment you'll want to raise the outfeed table against gravity thus putting tension on the mechanism. (Never back off an adjustment on any machine as your final adjustment.) As needed incrementally make very small adjustments raising the outfeed until it's perfect. Go too far, lower it back down and start over again. When set, lock the table and don't use the outfeed hanwheel. (Some shops take them off once set.)
Hopefully it should be cutting well at this point. If there is a slight gap in the middle of the joint, that means the table(s) are still a bit droopy. But wait! If it's just a couple of thousands, you just made a spring joint that once clamped will have the glue joint forcing the ends together. Almost every split I see starts at the end, and you've got the whole joint stopping that. (my preference).
Just an FYI, repeated jointing on the same edge will cause a taper to start even on a well set up jointer, especially multiple light cuts. Possible bad news is if your blades weren't installed perfectly parallel to the tables, you'll need to have the fence in the same position every time. I doubt it would cause a real problem face planning if that was the case. (you could always reset the blade heights, took me forever the first time) The above procedure takes me about 15 min tops, lots faster than my typing. Best of luck, feel free to ask.
