We recently put a new engine in our truck and it starts but as soon as you rev the engine up, it dies and won't start for several hours. The check engine light was on so we checked the codes which was the idle control sensor and the vechicle speed sensor. We replaced the idle control sensor but that didn't help. Don't know if the speed sensor would help. Any suggestions? Someone said maybe our ECM is bad?

as bad as this may sound, could be a bad fuel pump.

That was replaced just before the engine gave out

You may have to re-configure the ECM to the Motor since its a swap out.

We recently put a new engine in our truck and it starts but as soon as you rev the engine up, it dies and won't start for several hours. The check engine light was on so we checked the codes which was the idle control sensor and the vechicle speed sensor. We replaced the idle control sensor but that didn't help. Don't know if the speed sensor would help. Any suggestions? Someone said maybe our ECM is bad?

What motor do you have? Is it multi port or throttle body?
Have you checked the tps(throttle position sensor) that could be the cause. I would say the idle controll should be ok if it idles. Did you mean speed density sensor? IF so it could possibly be that. After replacing sensors it's a good idea to reset the ecm, usually disconecting the battery for 5 mins will reset it. Also pull and inspect the plugs making sure to note which cylinder they came from.

Well, we finally had it towed to a shop this past friday and picked it up today. One of the lifters was turned a little when it was put back together and the distributer was turned wrong and the wires on wrong. But thanks for all the help everyone. Hopefully this will help someone else.

yeah that'll do it..always remember the basics when diagnosing a motor.
Three essentials for a motor to run: Ignition, Compression, Fuel.