91 350 Sdl Vacuum Leak ????
 

My 91 350 SDL with 159K just developed this trans and heater problem at the same time. The AC quit working (no fan) and it only puts out max heat and there is no response with the climte controls at all, and also the trans will shift rough and it will shift into 3rd from 4th at highway speeds ????

Try taxing the vacuum system to the max operating central locking too. If it's total vacuum slow down, then probably the vac pump needs diaphram..... about $40 for rebuild kit.