mcx apex stalling after long steep pulls

[apache]

went riding on the weekend. sled ran hard, 18 lbs of boost, straight ave gas(full tank)at 8,000 feet. sled ran fine except right after steep long climbs when I would have it wide open for a while. right after making the hook to turn it around back down it would stall on me, then start fine on the bottom. never happened before. also, on the trail back I noticed the a/f was at 17-18.
any ideas?

 

[M5-]

Maybe check the fuel tank pickup in the tank?

M5

 

[julio]

fuel

also look at fuel filter and small boost lines especially to the controll box and atmospheric presure sensor. I am surprised it would run if your afr was that lean.. your sensor may be crapin out.. julio

 

[Tuesday]

Mine did the exact same thing when it was the fuel filter on my nytro. Could be possibly your fuel pump as well.