Wy My freightliner truck has no power when driving I change the egr valve and it still has no power when driving speed is low
Your truck could be having acceleration problem which can be best determined by a mechanic. You should contact your mechanic since he has the necessary expertise and experience with such issues and he will attend to it accordingly.
Maybe turbo system is leaking or otherwise faulty. Check all related connections. Also check air filter and fuel filter.