Why is my trucks engine always stumbling when I accelerate and when iM just crusing down the road

This is most likely one of two issues. First is a fuel issue so we need to start with this and find out what the pressure is and then we can go from there.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Once we know what the fuel pressure is when this happens then we can make a better decision.

However, if the pressure is ok then we need to check the engine for a vacuum leak which is the next most likely cause of this.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let's start with this and we can go from there, but I suspect we will find the issue with these two things.

Thanks