1998 GMC siearra 3500 diesel dully auto 4 wheel drive
my transmission will not shift from 1st. it has not ever slipped - seems to have the correct amount of fluid - worked perfectly when I parked but when I restarted the service engine soon light came on and it would not shift
From what you are saying, it sounds like your transmission has gone out. Your sun gear reaction shell has likely broken. I would recommend overhauling your current transmission or buying a re-manufactured transmission from a reputable company. AC DELCO makes good replacement transmissions.