JCJ

I had a strange problem this weekend and I would appreciate any feedback. I have a 2008 Suburban LT 5.3. I was on a road trip and stopped for a break in a small town. I got back in and it started, but seemed like it was choked for gas and then died. Then it would just turn over, but not start at all. A mechanic in the small town was kind enough to take a look at it. After telling him about it, he crawled underneath, and told me to turn it over while he banged on the gas tank. To my surprise, it started right up. He suggested my fuel pump was probably going out and I had vapor lock. He said it should only happen when its hot. For the next two days, I only drove short distances and it started every time. But then when I was ready to come home, it happened again. I tried to repeat the banging on the gas tank trick to no avail. A passerby saw what I was doing and I told him my story. He suggested I disconnect the battery and connect it again. I did that and then it started right up.
What a weekend! Is there any truth to these tricks? I'm planning on running it in to the dealer unless anyone has any other thoughts or suggestions. Also, what should I expect to pay if it is the fuel pump. Thanks!