Hi guys,

I have a 92 Dodge d250 Cummins diesel engine with a 518 trans. The trans will operate in first gear in drive or 1 manual and the reverse gear will work. Both engage positively and function correctly but the trans will not upshift to 2,3, or OD. I have changed the trans fluid but all of the pressure ports are still low in pressure. I think the pressure regulator valve may be stuck but I'm not sure. Can anyone give me some advice on what to consider or check so I can get this trans working again. I am new to trans diagnostics and repair but I would like to learn more about this skillset.