Code p1682 with driver 5 line 2 with code U0101 on 08 avalanche 1500

Question

my avalanche continued to run after I turned key off and removed the key. It ran till it was out of gas. I pulled up the obd and had 2 codes, P1682 and U01021. It also stated Driver 5 bus 2. When I restarted it would not show which gear it was in, no illumination of the P R D... and did not turn off after removing the key. This happened 3 times. It now does turn off but reluctant to drive as to not sure if I still have a problem. Where should I start?