Hello and welcome to the forum!!
I own 2 6.5 motors and they are great motors. The 6.5 didnt change from when they started making them and when they stopped making them. The only difference that Ive seen are some are turbo and some arent. The main problems I know of is the fuel pump injector driver goes bad and makes the motor shut off (happened to mine) The old driver is hard to get to but you can get a after market one that that relocates it and is alot easiar to replace and takes about 20minutes.
Second problem is the injection pump itself. These usually start to go bad after 120,000 miles +? No real time. There kind of hard to replace and you need a scan tool to adjust once the new ones on.
Other problem. The heads will crack under extreame heat. Not real common but possible.
Last known problem is the crankshaft can break in halph. This also happened to mine... Thats also extreamly extreamly rare.
What are you looking into? Good luck!!
2006 Silverado 2500HD LBZ CC SB
Exterior: Escalade Handles, Front windows tinted to match the rear, painted bumpers & mirrors, billet grille, 305/50/20 Cooper Zeons on BMF Novakanes Death Metal, Cognito Braces, Stainless Sleeves, Train Horns
Interior: 4 Kicker 10in Subs in 2 custom box's, Autometer Ultra lite II Pyro and Boost gauges, Aeroforce Interceptor Gauge, LED Lows & Fogs, Painted accents
Performance: EFI Live Tuned by Blackout Performance, Custom Blackout Performance S475 over stock twins, 45 over stock injectors, MBRP Turbo Back Stainless Exhaust (Straight piped), Raptor Lift Pump, AFE Filter, GMAX6 kit with Suncoast 1057 converter installed by Blackout Performance
1999 Ford F-550 PowerStroke ''Wrecker'' **Jerrdan bed, S&B Intake