Problem: Wall mounted oven will not reach set temperature at 300 degree and it take 30 mins to get up to 160 deg (max)

Tried:
- Check both bake elements continuity and they are fine
- Check temp sensor is fine (~1200 ohm)

At a loss on what to try next..
- Do I need to check or replace the thermostats? Which one? and how (what to look for)?
- Do I need to replace the controller/timer?

Any help will be appreciated.