Hello, first time Newb here. I rececently bought a 50th Anniv '99 Deville. I have managed to work off and clear all codes at the DIC except for a IPC U1255(Class 2 comms failure). Car has 160k Mi on it, and runs like a dream. The one problem I have left is I do not have Fourth gear on this car. NO other codes than above. The Valet switch is NOT engaged. 1,2,3&R shifts are smooth and great. driving down the highway at 57 mph and gear selector in OD, tach is showing 2250 RPM's. The car doesnt even attempt a shift into Fourth. Also, will NOT downshift to 2nd manually, just "free wheels". I have replaced Trans fluid, which looked black(Rut Roh), Replaced lower valve body, Fourth servo and piston pin, checked every fuse, front and back, and I am at my wits end! I have studied the tech sect of this and other forums on the 4T80E, and subscribed to alldata DIY. UGGHH... Please help.