leonesm

My uncle has an '06 with the 48RE that is lugging down when it shifts from 1st to 2nd. He says he feels like it's in the motor and not the transmission. I haven't actually ridden in the truck but he says it only does it on that shift. The truck isn't throwing any codes. He has been running a downloader on the truck but turned it back to stock and sees no change in the way it shifts. Is this the transducer and solenoid? What else could cause this? Thanks