P1199 fault code

[PARMY]

Hi, i have this fault code p1199, the problem only seams to appear when it is hot
Like the weather we have had the last few days,
The van runs fine till you start to go up any sort of incline and put a bit of load 
On the engine and then the van goes into limp mode, this is a problem that has gradually Got worse, since new the van has always had an episode every now and then of just randomly cutting out when you change gear from say 3rd to 4th it is like you have taken your foot off the throttle but it is pushed to the floor with it to only slow down and stop which is quite annoying,  i have changed The fuel pressure regulator on the pump and changed the filter
The fault reads
“P1199 Fuel high pressure regulation. Lack of fuel prevention strategy 
Intermittent”
Van is 2015 non ad blue 
Any fresh ideas or info, i would be most grateful  
Thanks in advance