1677-HO 1999-2004 Chevy GMC AM Gen 6.5L Diesel CCW threaded fan clutch water pumpThe 1677 HO is designed to outperform GM's higher flow rate "130 gpm" pump introduced in 1997 with the threaded hub. GM achieved higher flow rates with a 10% larger impeller diameter than the earlier versions. Most people simply look for that to determine if it it is higher output or not. We go a wee bit further. Our impeller outperforms and outflows to help the 6. 5L diesel run a little cooler under a load. The impeller has an increased vane count, a