Transmission will shift into 1st skips 2nd and won't go higher than 3rd

[Velocirichter]

My transmission in my 06 sierra 1500 will go from 1st to 3rd but will not go into 2nd or higher. I tried using the manual shift to go into 2nd but it refuses. There are no engine lights or codes that show up. I took the trucking fishing and there was a large build up of ice around the transmission. It wasnt shifting on the way back home so I let the ice melt and took it for a drive to see if that was the cause but it still won't shift. I'm just trying to get an idea of what might be the cause before I take it to a mechanic.

Thanks for the advice and I'll let you know how it goes