If I take off easy, it sometimes acts like it can not makup its mind which gear to be in. It seems to shift back and forth between 1 and 2 until the speed get up to about maybe 10 MPH. I notice this mostly when taking off from a red ligt and turning, so you do not speed up very fast. If I take faster, then it shifts as you would think it should.

So what controls the 1-2 shift?

98 3500 12v auto

 

Check the fluid in neutral and warm. Bring it to the top hash marks.
It may be getting air or have a plugged filter.
The 1 - 2 shift is all hydralic, no electronics.
How many miles?