isx cm871 overspooling

[Crash Dummy]

Hi , I have a ISX 425s 2010 kw t660 ,had the mandate removed March last year. All ran good, boost was the same as before. Bought the truck with 350k on the clock, but after dumping $10 k in the epa system to replace, 14 months later if fowls again, so did the mandate removal.
Blew head gasket 1 year after. Think head gasket was bad for a while due to one head bolt that had to be cut off to remove head, it being covered in rust on removal of head.
After Head replacement, cam bearings, and rod and main bearings, first load was showing well over 40 lbs boost, was never over 36 lbs prior. only other thing replaced was exhaust temp tube to exhaust temp sensor, it showed being cracked with tell tale "dirt" around tube except where it broke completely when removed.
I have now trashed 3 turbos in less than 40k miles. Sent last to shop to be diagnosed, result is over spooling. I was also thinking oil cooler plugged as the temps were rising late last year into early spring prior to head gasket going. so this time around, had oil thermostat changed before leaving repair shop for home shop, where i will have cooler replaced.
I am at a loss as to what is really cause of the turbo's blowing, i cant totally blame the mandate removal, as the motor performed very well for the year prior to the head work done. I feel it is something done or not done during the head replacement. any ideas with what i have stated since the replacement that affected boost and over spooling that was not happening before?