Faster and cheap heavy duty printer

1) We have Heavy Duty HPLaserjet5000N printer installed. Problem is that sleeve of it?s fuser assembly gets damaged/burnt after few months(2-3).And we have to replace it.Can u guess the cause of this and tell us precautionary measure for this?
2) 2ndly What heavy duty printer will u suggest for the circumstances of
a) text printing.
b) High speed needed.
c) Finance is a concern.
d) Is line printer suited for these conditions.
3) Line printer is suited for which conditions?