Cranking speed is a big factor in starting. Weak batteries and poor health will hard start especially when cold. Fuel supply and quality, age of injectors, IP, timing chain, engine??? Clean air filter?
But glow plugs are most common issue. What brand did you use and how old are they.
97 5spd K2500 Ext Cab short Bed ~160K miles.
TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.