Could scanning cause shift problems?

[87gmc]

When im data logging with black box it seems the 1-2 shift are delayed. When not connected to data port it shifts fine. Could the hardware be causing this problem? By the way its on my 99 GMC 5.3L Automatice 4l60 :?:

[Black LS1 T/A]

I've never experienced that kind of problem.

[GMPX]

When im data logging with black box it seems the 1-2 shift are delayed. When not connected to data port it shifts fine. Could the hardware be causing this problem? By the way its on my 99 GMC 5.3L Automatice 4l60 :?:

I just can't think of any reason this could happen.
If you had a separate trans controller on the bus whose shift messages were being delayed because of the scanner then yes, but that is not the case with the PCM doing both.
GM limit the amount of data the PCM sends back so it has time to actually run the engine and shift the trans.
Does it only happen when you are actively logging, or just when the unit is plugged in?.

Cheers,
Ross