With simplest things first in mind give the battery terminals and connections a real good scrub up , i pulled my truck apart once looking for a fault only to find out afterwards when i decided to clean the terminals out of boredom that one connection pretty much fell apart when i went at it with sandpaper , Roughtrax sell genuine Toyota connections and the maddening problem i couldn't find was fixed as a result .
Search the engine bay for a build up of black oil mist which would indicate a boost leak , fuel and boost are electronically managed on this engine so if your boost pressure is low it will also limit how much fuel is pumped in .
Another possibility is air in the fuel line maybe , happened to my 1kz after i had dropped the tank to paint it but i suppose it could happen if you had a leak in the line somewhere .
Starcruiser , fbnss and me managed to remove the air in a field in Germany with Rich pumping compressed air into the fuel filler cap , Nick pumping like a girl on the fuel filter primer and with me underneath getting a diesel shower as i replaced the flowing return line to the tank .
This could be ruled out by running a bottle of diesel direct to the pump .
I think its fair to say the 1kd is considered to be mostly bomb proof and in all my years on the forum the suction control valves have been the only reported weakness and even then there's been only a handful of reported cases . Mind you not many of the the D4D 90 series made it to the UK to begin with .