HELP needed with GMC transmission problem

My 2000 Sierra just started having a problem with a server jump from 1st to 2nd gear. When starting from a dead stop and my automatic goes from 1st to 2nd
on take-off, I get a very bad jumping jerk of the truck. All other gears are good.
To get around the problem I began starting off in 2nd gear from a dead stop.
Any help is appreciated. Terry in Texas
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A scan with a trans function scanner can look at various solenoid operations and look at pending trans codes, there is nothing external that can affect trans shifts as you describe.

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