My automatic transmission has been getting progressively worse and with the cold now flares too badly to reliably make the shift from 3 to 4 and even 2 to 3. However, when I disconnect the vaccum hose, it has no shifting issues except of course that it shifts very hard up and down. Vacuum leaks are not bad, doors, trunk locks work, etc. Any advice? Thanks. Also, the transmission fluid is burnt, but I'm afraid to change it given the state of things. Should I?