Whats Wrong with my transmission?

I have a 89 chevy 1500 silverado with a 350 engine. Ill be in drive and ill be going just fine until it needs togo into 3d gear then it slips. everybody has ben telling me different things and im wondering if there is a mechanic out there right now that can help out. ive heard it could be a vaccum line, the... show more I have a 89 chevy 1500 silverado with a 350 engine. Ill be in drive and ill be going just fine until it needs togo into 3d gear then it slips. everybody has ben telling me different things and im wondering if there is a mechanic out there right now that can help out. ive heard it could be a vaccum line, the linkage, and idk, please help me
4 answers 4