I think you have enough vehicle for the trailer you currently have. Shouldn't be a problem. However, the spark knock you are experiencing is a problem. That engine is designed to run on premium to make the performance advertised. That allows the computer to adjust the timing depending on the load as much as possible. The engine has a piezzo spark knock sensor that senses the knock and adjust the timing to eliminate it. Without the higher octane fuel, it can't get rid of the detonation. So power and engine longevity suffers. The other issue could be the sensor detecting the load on the engine. GM used a manifold Absolute Pressure sensor in the past located in an area that carbon could plug the hole. This prevented the computer from reading the loads correctly and would lead to spark knock on hills without affecting other driveability. Went to three dealerships before learning GMs system and fixing it myself.
