do the wheels spin freely when the engine is at idle or with everything not running. Are the brakes dragging or is a bearing locking up if that is the case. What does the engine sound like when taking off?? is there a delay (feels like a car trying to start in 3rd gear) in the transfer of power? does the clutch bell turn blue or purple after a long driving session.

My explanation if all else is ok... Screw it. If it runs well at 300-345' F and is smoking light a freight train then screw it and go with it. If the engine was actually lean as heck and Had an issue at 345' F then you would notice a loss in Power, low end, or notice the engine running awkward or improperly.