Doesn't sound right to me. HPOP doesn't care what temp it is outside other than the oil type your using. You would need a diagnosotic tool hooked up to the truck to see the HPOP psi on crank/start/running. Have you verified the glow plugs are actually working? You can check your battery voltage when you start the truck and monitor it for a few minutes you'll see the voltage draw down when there on and jump back up into the 13vdc range after they kick off.
99 F250 XLT,4x4,SC,SB,A/T,PMT1,White/Silver w/silver ARE LSII tonneau,MB Razor's,295-60-20 Nitto trail grapplers,Rhino Liner,Rancho9000's,Bushwacker Street Flares,DP Tuner,True-Cool Max,AFE modified-W.D.RamAir,5"Hypermax exhaust,Hypermax DP,Firestone Ride-Rites,2.5" front leveling leafs,AutoMeter-ProComps/triple pillar,heated TTT mirrors,DEI remote start,Amsoil enhanced.