I still havent put my DSP2 in either.
Even though I dont have a stock tranny anymore, I am considering putting in a drag tune and a regular 90 HP in the other slot.
Hit black ice on the interstate pulling a cargo trailer....
http://duramax.onlinedesk.net/photos/index.php?album=%2F2003%20Duramax%2FJanuary%2030%2C%202004
Yes, I'd do a 2 5/16" as well....and make sure you have the ball on your truck rated for 10,000 lbs (1 1/4") shaft.
For pulling my equipment around, I use a solid 2" receiver and the ball with a 1 1/4" shaft...the stock hitch will fail before it ever does. (See photos)
Nice trailer, I dont...