it's a 6.0 but any of these trucks with afm active on them don't have the potential to hit 300k hybrid or not in my book. it's probably been repaired once already to hit 215k or will need to be soon.
the hybrid battery in these are basically 3rd Gen prius cells in a longer pack. so higher voltage. they are 90s tech nickel metal hydride. the life expectancy is about 120k in a cool location before they start causing bucking and bad drivability. which is ******* everything. it probably has a replacement battery by now if it ran OK on the test drive. Google green cubes for the price of the batterys. they come swap them out for you on site I'm told.
the battery is probably the biggest thing of these hybrids, the afm is really a issue across the board. the tranny unlike the non hybrid ones that need the torque converter replaced around 120-150k before it kills the tranny. these are pretty solid, they don't have a torque converter to go bad. the down side is, most shops won't touch them. they will just tell you they can't get parts. they actually do make parts, there's a guy here that rebuilt his but I'm not sure if he ever got it running. he had to have a dealer program something for him, which is the 2nd down side. most shops don't want to fix these trucks, even the gm dealership are pretty bad about it. I see lots of people have a bad time with them at shops.
if you're mechanically inclined, enjoy interesting tech and willing to pick up a clone tech 2 scanner for if anything goes wrong I really like mine. if you're not, I have a hard to recommending anyone buy one of these Gen trucks with high mileage if they don't know forsure the afm failures has been addressed, hybrid or not.
I got it mine at 130k and it's at 160k now, I enjoy it. but I did ton of searching and knew basically what I was getting into, at least on the hybrid system side. the truck itself has needed more worn out parts than I expected but it's grown on me, I will hopefully hit 300k with mine. time will tell if I can