1978 Chevrolet Malibu fuel pump

If a broken fuel pump was not the reason for vapor lock breakdown on the freeway in 90 degree weather and then works fine when its cool, what else could it be. Ive replaced the fuel pump and have driven it in 75 degree weather, stop go hot ideling, the truck seems to work fine. After it broke down on the freeway it also broke down the next day in not to hot weather not on the freeway. The clear gas fillter was empty, after it cooled I was able to get it home. I went three more days before I changed the fuel pump but once I did let it die wile being hot with no fuel in the filter, does an empty filter make any diffrence or was it just a hot fuel pump not working