My truck will idle ok. But when you give it gas it will only take it slow, and once you hit a certain rpm, which is low, it automatically cuts off. We think it is a vacumme leak somewhere. I think it might have something to deal with the fuel pump also.??

Doesn't sound like a vacuum leak. Maybe the fuel filter is clogged? Try the Fuel Pump test listed here.

ddgonzal has likely hit the mark again.
If the filter is blocked up, or the pump is bad, you will find that enough fuel reaches the carb to fill it at idle. When you drive off, the engine consumes more fuel than the carb receives. The fuel level in the bowl drops & the carb runs out of fuel. Close the throttle & the carb fills up again.

If this is the problem, you will find that there is a maximum sustainable speed that you can hold. Any more, & the engine cuts. Any less, & it's fine. Change the fuel filter[s]. Sometimes there is one near the tank as well as one in the engine bay. Give it a try. If the old filter has water in it, buy two filters & carry one as a spare, you might just need it.