code 1 is no seat switch input, this would explain the problem with the seat. The seat switch and its ability to 'make' while sitting on the seat may be erratic due to wear. I would check it for resistance and also check the wire harness from it for any abnormal damage.

code 2 is forward switch is closed before the key or seat siwtch closes. This is showing because of the seat switch input issue.

code 6 accelerator pressed, no direction selected.
This means the accelerator pedal is being activated before the truck is put into a direction. If this is a monotrol system then it could just be another code set in place because of the seat switch problem. Or it could be directional switch issue also.

verify the seat switch is working first