Can't comment on the issue; however, you have found out that not all mechanics are versed in the older GWs, and as such, you will need to be your own mechanic. You need to get the OEM service manual. Trying to determine what has caused these new issues is a PITA, especially if these were not there before having the cables replaced.
I wouldn't use the cable replacement as part of the issue. I would look at the cable install and all wiring close by to ensure everything looks good, connectors are tight (loose connector(s) are hard to diagnose and can play havoc with the system(s)). Not a lot of room to work with sometimes and parts/components do get jostled. Work from the components back to the power source.
No one will be as particular about your bike than you.
Good luck. Cheers