Hoping someone can help me out-

I've installed a 2008 6.0 and transmission into a street rod. I have a timing problem. The engine runs proper timing at idle and part throttle cruise, but as you tip into the throttle the timing decreases significantly all the way down to the 0-5 degree range. I have shut off all of the normal things you would in a street rod type application. I am using the T42 TCM. I am using a E38 ECM with a 2007 4.8 liter calibration to get around the cylinder de-activation system.

There are no codes in the ECM or TCM, but I'm thinking there is something that it doesn't like.

Any help or educated thoughts would be appreciated!

Jim