allison transmission

I was going up a long pull. The trans. was doing right. It down shifted as it should and was not slipping. I reached the top of the hill and started down, as i got to the point to give it throttle it would not go. It was as if in nuet. Itr would not go in any gear. No change at all when shifted from net. to any gear. I checked trans. fld. I was on a slope so i added a little. It did not help. The fld. was clean and bright with NO burnt smell. I checked the elect. selinoid under and it is moving when the electric shift is shifter. It is in a 1988 executive 4 speed allison with a cat 300 turbo. Again, no burnt smell, fluid level ok, clean and right color. The trans was operating as it should just before it would not pull. (like it is in nuet.) Help...
Re: allison transmission

1. I assume the engine RPM going up as you gave it throttle? If not, it's an engine problem.
If yes,
2. Make sure the selector shaft itself on the transmission is moving as the shifter is shifted. I'm not clear which solenoid you are referring to. Allison does not provide these electric shifters.

I am guessing here, but it sure sounds like shifter, or detent shaft in transmission. Because you are not getting either forward or reverse. If you could only get drive and not reverse, fourth clutch would be failed. If you could get only reverse and not drive, forward clutch would be failed. However, first clutch is common to both first and reverse. But you say no indication of failure in fluid. Did you change the fluid recently?