I also believe pannhead to be on target here. Could also just be coincidence that it had been serviced recently. A $15 dollar vac gauge can save you a lot of money in the long run. Look for 20+ hg of vac coming directly off of the vac pump. Check the lines from vac pump to wastegate selenoid and then down to wastegate actuator for holes and rub-throughs (not uncommon).
Check codes if possible and see that it's not throwing any for your wastegate selenoid while your at it.

I'm pretty sure that the PCM will put the 6.5 in a catch 22 situation. Your pulling hard uphill....it creates heat...if the system (air, turbo, fuel, exhaust)is not in top shape it REALLY gets warm. The PCM notices hey, things are getting too hot here...cut fuel, cut fuel....you (frown on face) say hey...more speed please and ask for more fuel which creates more heat...and around the cycle goes.