Help, My Tranny Hates Me

I own an 83 Blazer K-5 and lately she's been having some transmission issues. She's shit fine when she's cold but as soon as I get to regular running temp she refuses to leave first, then finally refuses to go into gear at all. I just replaced the tranny filter and gave her all new fluid and treated her with Lucas Transmission Cleaner, to help with any leaks. (Has one by the front seal). I have done everything that I can think of to get her to move and be her functional self....help me I'm outta ideas!