cowboymck

I have a 2001 p/u 5.3 liter. Have 141,000k just had transmission rebuilt with b&m shift kit hd. I have a vibration/miss? between 40mph and 50mph. Never done this before rebuild. Took it back to shop and they say it is a miss in the motor. Tech said since trans. is running at full pressure now when the converter locks in it is pulling power on motor thus showing up a miss. So I changed original spark plug wires to see if that was problem,nope still same. Just got back from o'smilly's and used there scanner for any codes. NONE! Is this a trans. or motor problem? Please Help!!!