2006 5.9L megacab, 156k miles. With the engine running in park, engine idles normal. When shifted into reverse or drive, The engine loads up to the point where standing on the brake barely holds truck in place. In order to go back to reverse or drive, i have to stop at neutral where the engine revs to 1500 - 2000 rpms and then resumes normal idle. If you go direct from drive to reverse it goes into gear at high rpm. No engine lights on, (never been on with this problem). thanks for help