what plugs are you running? How many pounds of boost? The rpm range you quoted is where peak torque (and peak cylinder pressures) are in the rpm band for your setup. If you've got a wide plug gap it'll idle great, but you'll reach the point of spark misfire sooner than a properly gapped plug. This usually only happens when boosting say more than 1 bar.

Bad gas and fuel pump could happen but fuel delivery follows the HP curve, so I'd think it would happen later in the rpm band. If there was a problem keeping up with the fuel pressure, though, it would start in the 4k range.