1998 Chevy Express Shifting issue

Maintenance/Repairs
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1

I have a 98 Express conversion van and when I start the van and pull away the van has trouble shifting between first, second, and third. It acts like it hiccups before it changes gears. I have to manually shift between the first few gears until I get to 55-60 miles an hour, once I get there and slow the van back down it will automatically shift like normal. I will not have any other issues until I turn the van off, as soon is I turn it off something resets and I will have to get it up to 55 again to get whatever it is to click in to get it to shift properly again. I can’t figure it out any ideas???

2

Is the Check Engine light on?

And when was the last time the transmission fluid was serviced?

Tester