I just returned home from a 500 mile round trip vacation and when I pulled into town my tranny started acting up,when I stopped at the first stop-light it didn't want to downshift until I was completely stopped.Then when I take off it shifts through all of the gears into overdrive before I reach 30 mph,if I push down on the pedal it won't downshift but blows out black smoke and no power,if I manually downshift then it spits and spudders and acts like the timing is way out of whack.Any ideas would be great,My truck is a '94 chevy light duty 3/4 ton 4x4 with a 4L80E. I just changed oil and filter which was clean and not burnt with only minor shavings on the magnet,
thanks, Kyle