I just bought a 95 firebird 3.8l v6. My first f-body for only 600$
It has 89k miles and it passed smog a few days ago. Right after it passed smog the engine light decides to come on.

I took it to have it the codes pulled and this came up P1870.
I know it has to do with the valve body but i've been looking at this shift kit for a fix.

http://www.transgo.com/A1_4L60E-4L65E.html

My tranny is 4L60E auto.

The engine light came on for about 24 hours then turned off while i was driving it. It came back on about 24 hours after it shut off. and now it shut off today after being on for like 24 hours lol. When it shifts 1-2 it does shuttle a bit, i can hear the struggle but don't feel much of a slam at all.

I just want to fix it before it gets worse.
Any advice?
Shift kit or replace tranny or valve body???