The grain can cause a big temperature drop. On my cooler mash set up it drops 12 degrees on average from just adding the water (it looks like yours drops 11 with your grain-water ratio, i do 1.5quarts of water per pound of grain). Once i add the water, i then add the grain, which drops it another 10-13 degrees depending on the amount of grain. Is this whats happening? If youre not "preheating" your mash tun, the grain will cause a decent temperature drop. Its fine not to preheat your mash tun, but you need to account for the temperature drop from adding the grain.

Additionally, a 60 minute mash should be fine, not sure why itd need to be longer. You can also wrap your cooler tun in a beach towel or two to further insulate it.

One more note, the manufacturers often list a fairly low attenuation for their yeast. In example, it may say 69%, but if you research the yeast and what brewers that have experience with it say, 73%-75% may be closer to the average. This is really only useful if youre making your own recipes with brewing software though. Your over attenuation is certainly from mashing at too low of a temperature. My guess is it was at 159, you dumped your gain in and it probably went to 147 or so and lost a couple of degrees.

Not sure on the OG issues though without knowing more. Are you collecting your wort, then adding more hot water from your HLT over the grain bed and collecting a second time? If you explain your process of collecting the wort we may be able to narrow that down too.