transmission and gear shift

I have a 1997 Sierra that slams into gear from 1st to 2nd when warmed up. My check engine light comes on with a P1870 ( I think thats what it was ) code. I have been doing some research and have read many different solutions. Now, when it is cold outside, I've been having, once in a while a problem with the gear shift. It it like it's locked into Park. If you push up on it, it will then release and let me shift into reverse, drive whatever. Is there a connection between the two? Or do I have 2 different prolems going on here?

P1870 and harsh shifts usually means the tcc apply valve is sticking especially when warm.

Sonnex makes a kit to fix this or you can go with a Transgo Reprogramming kit that improves a lot of issues with the 4L60-E.

The locking in Park is most likely a different issue with either the linkage or the neutral-safety switch.

//2000CAYukon