Don't know what to do.
This is my first diesel. It is a 2007 6.0 power stroke with 70,000 miles. It has been babied all of its life. Everything is stock and here is my issue - On a cold start I have zero problems but after the engine heats up to normal temperatures my throttle becomes hesitant but only from the first inch and after I pass the first inch it comes alive. If I run the truck for 20 minutes or so and turn off the truck and then restart the engine it will only run about 200 to 300 rpms and if I press on the gas it doesn’t do a thing and if I press on the brake it dies. If I just sit there a few minutes the engine will start running up to 500 rpms and then 1100 rpms and then I am able to drive away. What in the world could be wrong? In advance thank you for your help..