2005 rail pressure
 

Ok I have a 2005 6sp with the in tank lift pump. I also have a smarty on it which I only use on level one. For some reason I lose power after driving the truck shortly rail pressure at startup and the first 5 mins of driving will reach around the 22k psi mark and then it's all down hill from the here dropping to around 3 4k psi. I have changed the fuel filter and the lift pump seems to pump alright but I do not have a gauge. I replaced the fca not too long ago maybe a month ago because the truck would stall and sputter which it seems to have fixed. Any ideas? Thanks.

Oh and also when rail pressure drops to 3k my boost will max out about 27 psi and egt will be about 1200, this is what most confuses me and as far as I can tell my oil level isn't changing.