#1 problem... if you have a fitting on there so you can attach either a 1/4" or 3/8" hose, the cap on which ever part your not using could be leaking (or the fitting that goes into the pump itselt). Pretty common thing to over look. Could also be that gauge them mentioned. Is there anyway to take it off and plug it?
#2 problem... bad hoses or connections?
#3 ... inacurate measurement (weak batteries or dirty micron gauge).
#4... really dirty pump. My POS pump would pump down to 300 microns, but it would take forever to get there. Yanked the front cover off, cleaned everything real good (there was a ton of rust and slime in there). Oiled it back up, let it run for 20 minutes capped off. Changed oil and now it pulls down much faster (still not as good as new, but much closer).
"If you call that hard work, a koalas life would look heroic."