There are many different versions of the th440 and 4t60. As long as you didn't swap in a 4t60e, which is electronically controlled, you should have no problems. The speedo issue is most likely due to a different final drive ratio in the replacement unit. The final drive ratio's range from a 2.84:1 all the way to a 3.29:1, so that would throw your speedo off quite a bit if you went from one far end of the scale to the other.