Stand & jab probably isn't in the gameplan since Diaz is a southpaw, the jab doesn't work nearly as well in the open stance since the range & angles are different. Jabbing is just asking for Diaz to slap down or trap the lead hand and open up with body shots.
The smart thing to do would be to kick the crap out of Diaz's lead leg and mix it up with some quick right straight to left hook combos, then circle out to the left after the hook and throw a right kick to whatever's open for a strike. You can pick Diaz apart all night long that way, especially if you have GSP's speed, footwork, and cage awareness. Add some Jon Jones style push kicks to the knee and Diaz will have a really bad day.