Here's a bit of advise I got from Quench regarding a Paragon I was working on.
This should help get your 5 volts up to par and keep it there.
"As extra redundancy there's some mods for the solenoid driver board which one caters for this weak point:"
http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Solenoid_Driver_Upgrades