hey everyone I got a 2003 Duramax and I have no forward gears it goes into gear but it slips through the whole gears but I have full reverse. I had a code for incorrect 5th geae but that was from before. Then i checked again this morning and had a vehicle speed sensor a ? P0500. Other then that i get no codes. I tranny flushed it, checked inside valve body for any debris etc. Changed the nsbu. I have no idea why i cant get a full forward gesr. Seems strange allllll the forward gears would slip, and that it would not go into a limp mode ?any help would be awsome ! Thanka !