6.2 have a very poor reputation being unrelibel, low power out put, hard to start,
6.5 are basicly the same enigne but alot more reliebel
many 6.2L have not been maintained proberly, poor fuel might be why they are so unrelibel
my 84 crew cab dually 6.2 na have been maintained all it life until for 10000miles ago it has 79xxx miles on the clock with original engine it even with non workin glow plugs 2 fully charged normal car batteries prober ground wires and new fuel it started right up, no knock, stuck injectors and no leaks on a never rebuild engine