Stalls after driven for 30 minutes

I have a 2000 Xterra SE 4X4, 2 weeks ago I had to change the MAF sensor and fuel pump. Ran fine until Yesterday. We went shopping 30 minutes away and when we came out of the store and got in the truck, It started and idled fine but when we would go to accelorate it would hesitate and surge. I took it to the shop this morning and put it on the computer. We monitered it driving down the road and everything checked out fine and wouldnt throw a code. To back up for a moment, when I started the truck this morning it ran fine for about thirty minutes before it started to act up(this is what is throwing me off). We unhooked the MAF sensor and it still stalled and cut out. We checked the distributer to make sure it wasnt arcing inside the cap. We checked the plug wires for damage and checked fuel filter. Now I dont know where to go from here. Does anyone have any ideas or have an xterra that has had this problem?