I have a 94 3/4 ton 2 wheel drive chevy that I have a problem with. The transmission won't shift(automatic). It goes fine in reverse and in drive it goes into 2nd gear and won't shift up. It won't go into granny either. The fluid is normal color and smell and the level was down a 1/2 quart. It hasn't seen any hard use...just a little bale hauling(small loads 50-60 small bales) Any ideas?