Perhaps the 5200 ft altitude?
Guess it's pretty hot there too.
Your pitch attitude at Vy when climbing out is going to be a lot shallower than what you might be used to at Vy in the lower lands.
One of the gotchas of flying in the mountains, there aren't many, but you just found one. Reach Vr, pull back, pitch for the attitude you are used to at 100ft MSL, stall, crash.
Get somebody who knows about mountain flying to teach you what to do. You might just kill yourself if you don't. Remember that at the shallower angle of climb you need to clear that mountain off the departure end, so feet per mile is what you should be thinking. Not feet per minute.
When landing fly the normal IAS numbers, but expect to spend more time on the runway before you can pull off. That's because your TAS is higher, you should know that, so go learn it. The gotcha is that you spend so much time on the runway that you run off the end. Don't cross the fence at 80kts, cross it at what the book says, should be around 65 in an archer.
Two mountain flying gotchas in one post. Not bad at all....