i cant imagine a modded 6.5 from what i have seen from the 2000 year 6.5s at work( maybe 2000 was a bad year for the 6.5s?). Rediculous for injectors, injection pumps and turbo repairs, not to mention auto trans failures, blow by from the engines, oil leaks, low compression and bad motors, but the ones i drove were work trucks with synthetic oils. I would be iffy of driving a stock one not under warranty or that wasnt a company rig.
Only to the ill-informed, Low compression ???, oil leaks???, turbo repairs ???, somebody was not taking care of ones you refer to, you do realize the 6.2/6.5 is same engine in Hummers & other military trucks, if as bad as you say they would have been gone long time ago there.
Properly set up 6.5 will do plenty of work and can make some impressive numbers on the track, mine pulls 18K loads, very good friend of mine just raced his a Bonneville only made 153 mph sustained appx 500hp at flywheel, same guy featured in Diesel power mag last month.
A set of injectors if needed is cost of 1 DMAX injector, if fed & cared for properly the 6.5 & even the 6.2, can be great to own vehicles, yes they will never make huge #s but many of us are happy with the "old IDI" GM engine. And mine will keep up & out do many of the stock offerings of Dodge & Ford, have been known to outpull/out run a stock early DMAX.
Alas where us 6.5ers can max out to on power, is mid level of others, so if big numbers are the goal 6.5 isn't for you, if you want a reliable Diesel power talk to someone that actually owns one & forgo internet myths & falsehoods, 6.5 can be made into a strong puller with modest track numbers if that is your fancy.
6.2 & 6.5 is only way to currently get a modern 1/2T with Diesel in it, 6.2 for economy, or 6.5 for power, I'm 200+ rwhp with mine, not a lot by comparison with what comes from a DI engine, but considering that is more than factory 195 flywheel rating less 40-50 hp lost through the drive train is not bad.
Many 6.5s still on the road, share many parts with the 6.2 so replacmentrs are inexpensive, military is still powering the hummer with the 6.2/6.5 so future is still good for sourcing parts for those that supply to military, guys like Heath, Kennedy, Westers, BD, are making some very nice aftermarket parts to enhance the 6.2/6.5 performance & reliability, also several sites like Diesel Page (1st 6.5 site) and Diesel Towing Resource (new but growing) with toins of 6.5 info by those that own & operate them on a daily basis.