My 1998 K3500 4x4 dually has a T400 trans in it that the previous owner swapped out the 4L80E. Everything works great except the speedo doesn't work. I think the T400 is a later model because instead of a mechanical cable coming out of the tail shaft it has a wired plug. I haven't traced the wires to the front of the truck yet but I'm assuming it doesn't work because the computer needs a specific signal and the T400 signal is not it. I am hoping that someone else has done this swap and knows what to do to get the original gauge cluster speedo to work....anybody?

For those who might ask "why did he swap the 4L80E for the T400?", I can't answer...except that after some research I see that the T400 is a much more reliable transmission than the stock 4L80E and asked a couple local trans shops and they said the "stock" 4L80E is yes a weaker trans and they need to be beefed up from stock for heavy towing.
I want to keep the T400 (to save money too) since I don't want to worry about burning-up the trans when towing heavy loads. I know it's not a huge big deal not having a speedo but it would be nice if there is a simple solution/converter etc.