Also any signs of coolant being higher than usual after driving(borderline overflowing)?
The coolant system pressurises when the engine is running, so the coolant level in the expansion tank will increase. It's shouldn't really overflow, unless you have trapped air that is now warm trapped air (which expands when warm) and the air is trying to escape. I can't say for sure.
You can always try squeezing the main radiator pipe between the rad and expansion tank. It's the old school way to try and purge air our of the system.
I can't properly diagnose it, so keep an eye on it. Also check oil is clean (no water contamination) as there could be other reasons over pressurising the coolant such as head gasket leak or charge cooler leak.
Hopefully - it's just some trapped air. When you replaced the matrix, how much coolant did you remove and then replace?