algy

I have just changed from a 90 to a 90defender tdi, I am v pleased with the extra power but when I start from cold it is VERY slow to warm up in that when i try to drive up my track which is a hill I am in first gear but when I change to second I lose power almost to the point of stalling then after about a half mile (which is all up hill) I suddenly feel a surge of power and everything is fine again, Any help would be much appreciated.

My defender is very similar to this until it warms up as are alot of older diesels i drove, I think it is normal cause as soon as it warms up the power is fine