I found a 3715 on ebay for $125. I was wondering if there was that much of a difference between the 3715 and the 3865 that i should pay an extra hundred or so dollars to get the 3865. I do know that for my truck, 98 1500 4X4 5.9L, the 3715 add says that you are not able to optimize shift points or transmission firmness etc. That is something that i really would like to have, but i honestly don't see the purpose of spending the extra 200 bucks for this feature unless all of the others are better/there are more options that are valuable. I don't want to rush, but the ebay auction ends in 2 days so a quick response would be greatly appreciated!