Running on the trailer with muffs I noticed I have much less water coming out the port side exhaust tip than I do on the starboard side. Is this normal on a hose with muffs? Stock 350/260HP mercruiser with log style exhaust into 90 degree elbow than out thru the hull. I pulled the port manifold and riser off, took the end caps and riser off the manifold and flushed it all out. Some rust came out but not too much at all. Reinstalled and still have the same issue. Could this be in the T-stat housing as it diverts cooling water to the manifolds and risers separately? Trying to cover all my bases so I will be installing a new impeller in the lower unit today. Anyone run into this before? Anything to check I have not thought of?

No problem, water will always flow the past of least resistance. On a hose, your not supplying the same amount of water as in the water. Even in the water, one side will be hotter then the other, just the nature of hydraulics