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...