tpaul,
I assume you're talking about the DGT6000 with 54 inch deck.
That deck is bad for grass buildup, especially wet and/or thick grass. When it starts glopping, you have to clean the deck out, preferably by removing the deck first. The high lift blades force the grass to the top of the deck so hard, they seem to splatter and stick to the top. You also end up with triangles of buildup between the blades in the front of the deck which spoils the deck's airflow. I've tried mowing slower and raising the deck--neither seems to help much. Once the deck is clogged up the only solution is cleaning.
The only thing that may help is doing a flush with water after every mowing job to remove the built up grass before it has a chance to dry. There are attachments you can get at Sears or Lowes that you drill holes on the back top of the deck on each side to flush the deck. The Sears package is the easiest to install, you drill one hole for the flush head and another for the retraining bolt to align the flushing stream. Those kits are regularly $19.95. Lowes has a different kind of kit for about the same price that requires you to cut an oblong hole to properly orient the water jets. These flushing ports are probably available at other power equipment dealers. Most decks seem to have them installed in the back top but I found decks with them installed in the ends and front tops. It probably doesn't matter, because all the water is whipped by the blades and forced throughtout the deck.
I have installed some on my 54 inch deck, but the jury's not yet in on how well they work.
I will post back here when I decide if they're doing any good or not. The first time I flushed, I did not flush good enough, some clippings were still left. I removed the deck and scraped it clean. (I had let the clippings dry overnight and consequently they stuck like glue.)
The next time I mowed, I flushed the deck thoroughly running the water and the mower until the water coming out was mostly clear. When I moved the tractor away from the cleaning area, there was probably half a bushel of clippings on the ground.
You should go to dealers and look at the flush ports so you can get an idea how they're installed and whether you want to go to the trouble of installing them. (You need two on big decks.)
Runningbare