Duramax engine/trans calibration probelems

[QUASAR]

My cousin has a 2001 Silverado, Duramax/Allison. Truck is great untill it starts to experience elevation changes. Did it 3-4 years ago out in Arizona now its doing it again in Pa. Check engine light comes on as soon as you start going up and down mountains, then it goes into some sort of limp mode where it wont/cant go above 65mph. When the problems occur it has alot of trouble shifting. GM dealer says theres nothing wrong and charged him a bunch to "reprogram" after this happens and it fixes the problem, untill he goes into the mountains again.

Any Ideas? I'm not famillair with Diesel systems and sensors that are involved. MAP related?

 

[KING302]

I would check here. http://www.dieselplace.com/forum/index.php?

My 05 did not like the Edge programmer. The Allison can be finicky at times, mine was programmer related.