lifter problem

i rebuilt my motor. yes a stroker anyway i bought a stage 2 head and all that i put about 30 miles on it and it just started to sound terrible so i thought i bent a valve or something. the shop that built my motor took care of everything and found that no valves were bent but the lifters were all impacted with oil and wasnt flowing the oil through them does anyone know why this should happen and why that fast or anything to watch for. im runing stock lifter but now im going to order the 3mm so that i shouldnt have to worry any more but i had 140,000 on my last motor and that never happened