2004 Chevy Avalanche transmission

2004 chev avalanche with towing package, and trans cooler. After driving about 3 wk ago I stopped at stop sign, and when I took off trans acted like it was in 4 wheel drive. Checked the panel and it was 2 wheel drive. Felt like it wasn't shifting. Pulled over and stopped and started in 2 nd gear, then to 3rd and then to drive and it shifted roughly. Pulled over again shut car off waited for a minute and stared car again and ran fine and shifted perfect. Ran fine for a couple of days then happened again, shut car off for 30 seconds and back on and again fine. No dummy lights or messages on car. Checked the trans fluid it was very dark, a little dirty, and in cold zone instead of hot zone. Went to dealership had trans flush, new fluid, and new filter. Before I got out of parking lot check engine light came on with no problems shifting. Took it back to dealership who stated codes stating tcc and 2-3 shifting selnoid are bad and put on full electrical check that further stated ignition switch not giving power to above selenoids. Is this possible. How to tell if selenoid bad or ignition swith bad. Have had minor issues over a year ago, 1. Radio went out replaced fuse and fine and fuel gauge sensor went out. Anne S.