Help!

Last week as I was leaving a stop sign (my car was at about 20 mph), the gas peddle felt like it had been sucked into the floor board and it lurched, but did not go any faster, the check engine light came on and then it stopped. I was able to restart and pull to the side of the rode. I maintain my car very well because it has had an oil leak since '99 when I purchased it and I take very good measure to make sure all fluids are good. I checked them about a week before this happened and they were all good. When I looked after it died though the water reserve was filled with sludge. I got it towed to a mechanic who said that he sucked the sludge out and there was no sludge in the radiator (good news). There was no evidence of cracked head/block or anything else, but the car had gone into limp mode. He told me he was going to take it to someone who worked on transmission... Any thoughts on what it might be?!?!?