By modifying the seedlayer in perpendicular FeCoB/MgO/FeCoB magnetic tunnel junctions (MTJs), we observe an increase in maximum tunneling magnetoresistance (TMR) from 65% up to 138%. It's found that decreasing the Ta deposition rate in Ta/Ru/Ta underlayers allows for greater annealing temperatures (up to 350 ) while still maintaining a perpendicular easy axis. An improvement is also seen at a lower temperature where both seedlayers maintain a perpendicular FeCoB easy axis indicating that the increase in TMR is not solely related to annealing at a higher temperature.