Any chance of you hosting the saved game somewhere so I could download it?

Things to consider:

- Capital. Have you moved it to a central postion. To reduce corruption and disorder

- 'Taxes as high as possible'. If thats not 'very high' then its not high enough. You can run cities on 70% public order. Thats red face. No lower though. I sense you dont micromange so such an approach carries risk as you may not want to check every city every turn..and with so many I wouldnt blame you.

- Are you killing rebels? They could be reducing the value of road trade.

- Did you trade with any who are now your enemies? War means loss of trade income.