Random stall 1 hour later it started back up?

Hello, I just found out about this website and already, I'm impressed. Hopefully you can help me out. I just bought this car, not long after it stalled on me while I was on line at the DEQ. Then about 1 hour later it started back up and got me home. Since then, it's stalled about 3 more times. Same as before, I would wait about 1 hour, and it will start back up and drive me home (I usually don't drive too far). I took it to a shop and paid for a diagnostic. They said it was my cat converter, and my 02 sensors were fine. I changed the cat (my car has 2). Drive it for a few days, then stalled again. I changed my MAP sensor, thinking that was the problem. It wasn't, stalled again. When I first got the car I did a tube up on it. All the spark plugs looked really bad. Changed them all. The last time it stalled on me, I plug a scanner in and it gave me a P0088 code. So now I'm thinking that I may need to either replace my HPFP or my fuel pressure sensor on the fuel rail. Hopefully it's not the lure pressure fuel pump but I'm not sure. What would you suggest?