Hi Jack,
Sorry for the delayed response, but here goes.
That was a lid temp I was reporting, and I wasn't using the Guru. I've seen a lot of post about the Guru lately and it sounds like it is worth checking out.
I used water for the cook. I don't have any sand right now, but I plan on picking some up.
This was easily the best cook I've ever had. The lump charcoal was AWESOME!!! If I can help it, I'm never going back to Kingsford. In my opinion it was easier to light, easier to maintain a constant temperature with little or no intervention from me and burned longer than the Kingsford I usually use. On top of that the meat was very tasty.
Using lump I maintained a constant lid temp of 220 - 240 degrees for the first 15 hours with no problems at all. I went to bed at 1:00 and the temp was 220. I woke up at 7:00 and guess what... the temp was still 220. After 15 hours, I boosted the lid temp to 260 and held it there for another 5 hours.
I'd say don't let the "Hard to control temp post" get to you. Use the lump and see for yourself. It is all about airflow... Al is right on the money with his post.
Take care,
John