2004 Duramax Diesel: P0735 and P0732 Fault Codes Causing Random RPM Spikes Under Light Acceleration

Hi everyone, I'm having a strange issue with my 2004 Duramax diesel truck. Recently, my engine has started exhibiting random spikes in RPM, especially during light acceleration at any speed. The problem occurs sporadically and can be triggered by factors like loud music if I don't catch it early. When the spike happens and I don’t react in time, the vehicle throws a P0735 diagnostic code — indicating an incorrect gear ratio in fifth gear. Recently, for the first time in several weeks, I also received a P0732 code, which points to an issue with second gear. I’m currently considering possible causes such as faulty shift solenoids, speed sensors, or even issues within the transfer case. While I’ve read some forum posts suggesting the transfer case could be involved, it’s still unclear how directly it affects these transmission codes. Notably, my transfer case started acting up before any of these symptoms appeared, which has made me suspect a connection. I’m looking for input from experienced owners or mechanics — any insights into whether the P0735 and P0732 codes are linked to shift solenoids, sensors, or transmission components like the transfer case would be greatly appreciated.