P0496 could explain your hard start condition after a fill up. It's usually a Purge solenoid but could also be a plugged canister. It Requires proper diagnostic to determine if that's the route cause. See here...
http://www.obd-codes.com/p0496
P0650 Is a fault with the MIL Circuit. It's possible the cluster it self has an issue. If the oil pressure gauge goes haywire again It could be a sign the Cluster is the issue. Cluster usually have the stepper motors go bad and occasionally the solder joints can crack on the board causing other issues .
http://www.obd-codes.com/p0650
Your hot air issue is usually the blend door motor. It's common on these trucks.
You also need to verify that the AC system is working properly and that you don't have a low charge or a bad compressor. You need to go to someone who specializes in this. It requires AC gauges, system knowledge and a specialized factory style Scan tool or equivalent to monitor data. It can also be used to test the Actuators in the system Via Bi-directional controls.