Truck losing power

Hello,

One of the most common causes for low power output or limp mode is having a dirty throttle actuator. Dirt and debris can impact the effectiveness of the throttle position and other sensors and that can trigger the limp mode.
Cleaning out the throttle body can improve drivability.

https://www.2carpros.com/articles/throttle-actuator-service

As for the white smoke, does the vehicle overheat?
Typically, white smoke is due to a blown head gasket. In which the coolant will mix with oil and create smoke. Also, this will turn the oil to a milky white color.

Here is a helpful guide on how to test for blow head gasket:

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know of any questions.

Thank you.

Inspect the throttle actuator and clean it out, if you haven't already.
Does the running issue only happen after the truck warms up or all the time?

Is your check engine light illuminated? If so, do you know what code(s) it might be producing?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Sounds good. I want to see if that might give us a hint.