if fans are failing, the ECU cuts boost due to overheat condition. suss fans first, then worry about boost.
is heater still functioning normal. if there is H/G issues, heat output will go up and down. check to make sure no mixing of coolant in with oil (brown foamy goosh on dipstick or under oil filler cap)
check coolant for oil contamination.
stay calm, check things thru and thru.