My 2nd grader has the exact same PSI as well although he has a 5pt spread between PSI subtests so I read that it's hard to draw any meaningful conclusions from that - could just be one bad subtest bringing the PSI down. I don't think he's HG though somewhere in that grey MG/HG border but he sounds very similar.
Most of the time it seems his clock runs slower than every one elses when it comes to tasks. He has no sense of urgency. Well, he was completely different on vacation w/ the grandparents. Every morning he bounded out of bed, got dressed, brushed his teeth and was ready for that days adventure lol.
I don't see it so much w/ academic pursuits though. He's not super fast w/ math problems but several of his classmates have said each year that Ds usually finishes first and gets them all right. He's not a HG+ kid though doing 4 digit addition/subtraction problems all in his head. Sometimes computation takes him longer b/c he will find the most convoluted way of figuring out something when simply estimated to 100 and subtracting 2 would get you there much quicker lol.
I still wonder what does this all mean if anything.....