Engine light and cruise control light stay on as i drive

Try by checking the cruise control relay as well as the fuses.The relay may be getting hot and shutting down.

code p0320 refers to cam shaft position (CKP) sensor/engine speed (RPM) sensor--circuit malfunction=== causes --wiring--CKP/RPM sensor ---ECM
because the engine runs ok until it is on cruise control I would be investigating the RPM sensor for a fault
The cruise control takes its control from the RPM sensor and if that circuit is interminable the the cruise control doesn't know what rpms to maintain.

When you have a check engine light come on, the traction control light and the cruise lights both come on as well. You need to have the codes checked with a scanner. There most likely isn't a problem with the traction control or cruise systems, the lights turn on because those systems work together with the engine management system or PCM. When there is an engine problem that sets a code that turns on the check engine light, it automatically disables the cruise control and traction control for safety reasons. Because the last thing you want is to have an issue with traction control and/or cruise control if your engine is having an issue, which is why they are disabled. The most common problem that turns on the check engine light is a loose, cross-threaded, or snug but not tight enough fuel filler cap. Subaru recommends three clicks of the cap to be considered tight. Also, any parts store can and will check and/or clear codes for free. I hope this info helps!

Same as the last time you got a MIL lamp on any vehicle

Check for codes,look them up & diagnose the system that
set the codes & then component test

Sounds like a short in the brake light switch test it replace it.

Your dealership should have seen any underlying codes. Most Cruise controls I've worked on are used on the vehicles vacuum. that is where i would start, because on a grade your engine uses more vacuum pressure thus taking from some where else.

The reason any cruise control will not stay engaged is cause by 2 things.

1. Brake light switch. Check to see if your brake lights are coming on when your driving.... i.e have some one follow you while driving without the brake on.

or

2. Loss of speed sensor data to the control module. The speed sensor on an automatic transission car is located on somewhere the drive train / shaft. On a vehicle with a standard transmission the engine tach signal is used. (also unsed on automatic w/Over drive) If you do not see a tach reading on the instrument cluster I would suspect a tach sensor problem.

Troubleshooting needs to be in these 2 areas. As far as a source for schematics. Clymer and Haynes are 2 of many after market repair manuals.

cruise light automatically comes on when there is a malfunction that causes c.e.l to illuminate,this occurs because your accelerator is electronically controled

get a scanner check code sound like vechicle speed sensor.