Was it ever soft after doing a lot of turns or going over a rough area? I have had this before and it is from the wheel bearings being a bit loose. Wheeling over rough terrain giggles the wheels/hub/rotors slightly (since they are all attached) and moves the brake pads out a bit. So that first press on the brake pushes the pads farther in to reach the rotors. This is why the second pump is normal. Check your wheel bearings for some play.
If this only happened when you first started the truck, then you may have some other problem.
1955 Series I
1994 Defender 90 #916
1967 Lancia Fulvia
1974 Alfa Romeo GTV