Lots of debate here, but nobody has actually answered any of this poor bustard's questions.
One answer, anyway: You are supposed to select the inboard fuel tanks for climb, descent, and manoeuvering, as that is where the boost pumps are. (? I think. 20 years since I flew one.) But that in itself can cause a problem - a multi-leg flight with lots of climbs and descents and turbulence keeps you on the inboard tanks, and on one occasion I had just levelled in the cruise when one engine got awfully quiet before I could select the outboard tanks.
