Go look at the fuel lines and see if there is air or fuel in them...it sounds to me like you have a leak which is allowing it to "lose its prime" which happens especially below 1/2 tank and worse if on an incline with the nose up. If you have air in there check the prefilter o-ring.

I still would not rule out glow plugs since that is what is sounds like to me, but since you say you had them serviced last year it may be more likely air in the lines. I would not say at 40F you need to worry about fuel gelling...it's much colder than that here and we've had no problems and never do.

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz