2005 Chevy C4500 8.1L LCT1000 transmission. All shifts are late, main line pressure is high spikes up to 350 PSI, Hooked up the scanner and it will not complete the calibration process. No codes, oil clean no debris in the pan.
Don't know about an allison but most other transmissions that would be related to a problem with the proportional valve that controls the line pressure?
What exactly does that mean? Comm failure or something? I had a TCM go bad on a 3000 series a few years newer so don't count that out as a possibility. "They" say computers rarely go bad but it happens more often than it ought to.