2006 several issues?

[Will308]

Hi.. been a long time since I was on this board. Got my daughter's 2006 X5 with sport suspension back and it had several issues. Did the search but nothing conclusive as it seems these are not straight forward issues ( intermittent). A little background. While I was working on it the drivers window began to slow down. Replaced the regulator (used the URO with the upgraded rollers) Replaced the valve cover with an aluminum one to correct a nasty oil leak. Worked great ( e-bay item for the M54 ). Next was chasing a coolant leak... so hard to find but we narrowed it down to the thermostat housing.. replaced that too and, now no coolant leak. But 2 items came up. When I first start it everything is fine... after about 20 minute of highway driving the check coolant level and the 4x4 light come on..( trying to remember what the display says about that.. think it's 4x4 inoperative) I don't hear a sound when I turn the vehicle off so I don't think it's the 4x4 actuator or gear? Park it and when I restart it.. nothing.. everything is fine....h until I drive about 20 minute and again I get those warnings on the display??? Anyone know what might be causing this?