Help Troubleshoot No Crank/Start '16 Sierra

[KBoy420]

Can you guys offer any suggestions or tips before I go to stealership? '16 Sierra Denali, 40,100 miles.  I bought it 3 weeks ago with 39,800. Randomly displays 'service theft deterrent system' and I cant start.  Dash lights up etc, but cant start.

 

Have had to use oem remote-start as a work-around, but that isnt working now either. The engine will start but as soon as i put the key in, turn to 'on', and put in gear, engine kills. 

 

Battery is original, but good. Reading 12.6v engine off, 14.1v running, and load test is good.

 

It seems to happen more when stoping/starting over short periods, like starting 1st in morning fine, go to get gas, turn off 5 min, wont start. Get it startedz drive and stop at ATM.  Turn it off 2 minz wont start.

 

If it matters my Infotainment outside temp is never correct either - and i mean off by a lot.  

 

Any ideas or suggestions?

 

Thanks guys!

 

PS - did new sierras come with 2 keys AND fobs? Dealer gave me 1 key and fob, and 2nd key by itself. Said GMC only gave 1 fob (and 2 keys) to new purchases.