I had a remanufactured transmission replace the one that pooped out on me and now the speedometer says I am going 100 mph when I am going 20 mph. also my truck won't go more than 20 mph. A mechanic said to replace the speedo sensor and I did. That didn't fix it. Now he wants me to pull the sensor from the differential and clean it off. He wants me to make sure there are no metal shavings on it. Any clues as of what this might be and how to fix it?