Can a plug under the dash cause communication problems PCM and 2-3rd Solenoid? on 1994 Chevrolet Suburban 1500

94 Chevy Suburban 350 5.7 4 wheel drive..
My husband put in a CD player in the truck in February. Under the ash tray there is a box with plugs into it. He re plugged everything back into the box and put the dash back together. He found a plug hanging that didnt get put back. Since them my truck is getting 9 MPG. A transmission guy today Diagnosed it but my husband keeps telling me that this plug hanging could not be the cause of the miscommunication between the PMC and 2-3rd Solenoid. All the problems I am having with 1st, 2nd and 4th gears not shifting and only being able to drive in 3rd started right after the CD player was put into the truck. Can a plug under the dash not being plugged in cause communication problems between the PCM and 2-3rd Solenoid in the transmission?
Thank you so much for your help with this..

Asked by for the 1994 Chevrolet Suburban 1500
ver common issue with gm veh. see free diag and est at aamco then shop prices
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