Also Peter, if your truck has the Automatic cold start Device (ACSD for short), a cartridge on the side of the IP with two pipes going to the engine block, these can sometimes break their part that is inside the pump. It can be removed for inspection or removed altogether (search ACSD on here). It advances the timing and brings up the idle for cold starting. If this has broken, the broken part can cause damage inside the pump. As this acts on the advance mechanism inside the pump it's possible it could have jammed it or otherwise affected it. Could be worth removing and inspecting it. It's only three bolts and a lost pint of diesel.