Bad EGR cooler?

[cantrucker]

So here is my long dilemma. A couple months ago my truck started acting up, it had very little power and would die immediately on hills (speed dropped to 25 mph up a some hill even with consistent down shifting). Took it to the shop and they changed the turbo, EGR valve, exhaust manifold (because it had a leak apparently) and the VGT controller. Still same problems then I took it to another mechanic because I was fed up with throwing parts at the truck. The second mechanic changed the charge air cooler and bingo the truck ran much better and gained back some of the lost power although it still struggled up hills at times.

Then a couple week after I took the truck back because I had developed a oil leak in the valve cover gasket and asked him to fix it. He fixed the leak but as soon as got the truck back and drove in on the highway the truck started to smoke like crazy under acceleration and coolant temps reached 220F & the loss of power was back. So I took the truck back and now he's telling me the egr cooler is gone and the truck is derating due to excessive egr temps.

So is he telling the truth? Or could he have messed something up when he was replacing the valve cover gasket. Should I go ahead and replace the EGR cooler at this point or get a second opinion?