Jim, Are you using all 4 channels of the TIU set to fixed ? Are you running wires from 1 DCS channel and then splitting it again to your powered blocks ? By powered blocks I'm guessing you mean terminal strips. If you have 4 powered blocks. You are better off using all 4 outputs. One feeds each block. Jumper the inputs of the power going into the TIU. One handle side would power both a Fixed and variable channel. Set the Variable to Fixed.
When doing your signal test. When you leave the block that is showing 10's. What do you have for a signal when entering the block you lose control in ? Are there any TMCC engines or passenger cars parked in the blocks where the problem is ? The fact that you switched TIU outputs and the problem is still there. Would seem to rule out the TIU.