I run Amsoil 15w-40 Max Duty oil and SDF24 filter. I do run it more than 2500 miles per change as it is a far superior oil and filter than what was available in the '80s when the engine was developed (they ALL are). Oil usage (loss) is a quart to 5-6k miles running empty. Excellent for this...
I have an Airdog on mine with the stock 10psi relief spring. It's enough to bump timing at idle and that is about what it sounds like at 30 Farenheit until the cold advance goes off. Then it is considerably quieter.
@Big T, right at the summit where your last pic was taken, there is a wee little sign about 100 yards off the road. I just had to know what it said, so I ran out to read "Beartooth Wilderness". I was a little disappointed!
I don't believe the 6.2-6.5 was a bad design. However, the execution was pretty bad. If GM would have built the engine that Detroit designed, a lot of the conversations on here would have never happened.
Torque.
I used to tow with a 350 (four barrel), TH400, and 4.10 gears. Occasionally would use a K3500 (454, sm465, 3.73 gears on 215/75R16). The 350 would pull if you kept it between 35-4500rpm. The 454 was gutless. A stock 6.5 is as well. However, if the 6.5 is healthy internally, $2k worth...
In the tractor pulling world, it is not uncommon to ring the block and run without head gaskets. Might not be possible with the cups. Is it necessary on a 6.5? At some point it will be for those pushing way past tty bolt clamping strength (Twisted Steel, Littleboy, CDD, and the young fella out...