I had a friend swap out a transmission for me when my other one had a bad differential. The used one he put in has a jolt from 1st into 2nd and then it slips from 2nd into 3rd but only when cold. After it warms up it functions normally. I have tried changing the fluid but it doesn't seem to help. What could else could it be? Torque converter? Valves? Solenoids?

First question on a trans swap..... assuming it is AWD, are you sure your rear differential matches the transmission ratio?

 

What model and year soob are we talking about? The 1-2 hard shift is often mentioned on the 90's models. Sometimes people say the dropping resistor (which helps modulate line pressure) can cause that.

 

2-3 shift 'slip'. May not be a true slipping, if the RPM is just flaring between shifts, it is probably the band adjustment.

Its a 2000 Forester. The transmission is exactly the same as the other one. Since both problems are only present when the car is cold and they also both go away when warm, I figured the same problem is causing both. Would "band adjustment" cause both problems?