Cracker,
Welcome to the Forums!
The GM 6.5 is a Detroit ... Here's a quote from content side of TheDieselPage.com ...
"Designed as a diesel engine from the ground up by the Detroit Diesel Division of General Motors, the original 6.2L diesel engine was introduced in the 1982 model year GMC and Chevy C/K pickup truck and full-size SUV lines. Taking this engine design to the next level in the 1992 model year, the new 6.5L diesel engine was an advancement in technology, and was designed for the application of a turbocharger. The 6.2L saw its final year of production in 1993. While the 6.5 was replaced by the Duramax 6600 beginning in the 2001 model year Chevy and GMC vehicle production, the 6.5L diesel engine continues to be manufactured and sold by AM General. AM General is the manufacturer of the civilian H1 Hummer & military HMMWV. Not to worry, support for the 6.2/6.5 will continue to be a big part of The Diesel Page well into the future."
Regarding Oil Change Interval (OCI) for the 6.5TD, I think 7K is on the high side (my 2 cents ) ... I used a 4Kmi OCI with AMSOIL 15w40 Synthetic in my 98 6.5TD ...UOA (Used Oil Analysis) results at this interval were good.. Rotella 15W40 or 5W40 may hold up for 7k but you might want to consider a UOA at 4 k then one at 7k to verify wear metals, soot, and and TBN are still within acceptable ranges..
Also check out BobIsTheOilGuy.com
Bill
03 2500HD D/A CC/SB/4WD,OilGuard, MegaFilter,LiftPump/PreFilter, Bilsteins,RetraxRollTop,J&J Boards,Coolant Filter,AlliDeepPan,FastIdle,AllHeadLightsOn,
98 K3500 6.5,SOLD