2013 w/D13 engine. What is fault code SA 16 DTC PO 29900?

SOURCE: P1211 DTC

Loss of power, usually after a hard acceleration; Rough idle; Check engine light comes on, DTC P1211:
Intermittent high pressure oil leakage.
This condition usually occurs when the vehicle is cold and the oil is thick. When performing a hard acceleration, the truck suddenly looses power, the check engine light comes on, and once returning to idle the engine runs rough and won't accelerate. Cycling the key may correct the concern, clearing the code from the PCM will correct it temporarily. If you can monitor data stream, at idle the ICP pressure normally is 400-700 PSI and the IPR duty cycle is 9-14%; at cruise, ICP is 700-1200 pSI and IPR is 15-20%; under normal acceleration, ICP is 1200-2000 PSI and IPR is 20-30%; and under WOT accel, the ICP is up to 3600 PSI and the IPR is 35% or higher. When the above symptom occurs, typically the idle ICP reading will be normal, but the IPR duty cycle will be high--over 20% and up to the max 50%. A "blow-by" condition has occured somewhere in the HP oil circuit. If you can get the problem to re-occur with some frequency, the most probable cause is worn or deteriorated injector or IPR o-rings. If the problem is intermittent, it could be a sticking IPR valve. Replace the injector o-rings with the latest-level kits--F8TZ-9229-AA. When replacing the IPR, make sure you get the correct part for the build date/serial number of your engine.

SOURCE: Check engine light/gas cap will not stay tight.

yes the gas cap could cause this,also check evap. purge solenoid and hoses for cracks or kinks,the solenoid is on the inner fender and has 2 hoses, one to the intake and one to the canister, the most common cause of this code is a defective purge solenoid.