Check Engine On Tranny Stuck In 2nd Help!

[BIGOLMULEY]

So I drove my 2004 CC Duramax up hunting yesterday. When I came back to drive home my check engine light was on and my gear indicator was off. Could not tell which gear I was in, other than by counting over. I put it in drive and could go about 40. Stuck in 2nd. I had reverse as well. I drove it back to camp. Next day I drove it back up the road, when coming back after hunting again it worked just fine for about 10 miles. I stopped at a light and the gear indicator light went out and 2nd gear again. What is up? Today I had to drive it home and it worked fine, other than the check engine light is on. Taking it in Monday. I am hoping some sort of sensor is out?

 

Buddy has a 2001 ext cab with 8.1 and same thing happened to him. $300 for some sort of sensor. Anyone else with this problem?

 

Jason "The Big Ol' Muley"