A couple of days prior to my current situation my trailblazer was skipping (or jerking forward) driving right at 55-60mph and I just assumed it was a spark plug issue, i got home truck sat for about 2hrs.I got back in to run and errand and I noticed a sound like it was a loose vacuum hose going down the road, i stopped at a red-light for about 45 sec. But then I tried accelerating but the truck wouldn't move at all just a slow coast like it was in neutral but I was in D gear all it did was rev up. I switched to reverse, 3,2 still nothing, however I couldn't get it to shift into 1st. But park works fine, I switched the truck off and tried it again. the fist 2 attempts made no difference, but the third time it went into reverse and drive gear. Went down the road about 100 ft stopped at a stop sign and it happened again no movement in any gear. I shut the truck off for about 20 min and tried it again it worked normally for about 2 min and no movement again. I've checked my trans fluid it's topped off.. I have no idea of what is going on?? Any suggestions welcome...