When you delete the egr cooler, and still use factory programming, the truck will actually lose some power and be in a mild detuned state. This is because a functional egr system is designed to work with the turbo and fuel program mapping with stock tuning. Custom tuning can bring everything back into proper function with an egr delete, and a using an SCT X3 type tuner with a custom heavy tow tune will make the truck run very well.
A functional egr system on a diesel is designed to help lower peak combustion temps in the cylinders to help control the formation of nitrogen oxide gasses(NOX). NOX is formed at combustion temps above 2500F, but this only happens for a split second and will be dramatically cooled by the time it exits into the exhaust manifold. The drawback of an egr system in a diesel is it causes hotter intake air and bad carbon buildup in the intake manifold tract and intake valves due to the mixture of exhaust and oily pcv gasses.
The positive of retaining egr is that it keeps high combustion temps and peak pressures lower in the combustion chamber, this is because egr is an inert gas(one that is depleted of oxygen). Egr gas is a filler that takes up some the space of the oxygen entering the combustion chamber. By doing so it lowers the formation of NOX, which is the only real reason we have it on all modern diesels, as they have not figured out any other way to control NOX formation better to date.
You can also just block off the egr cooler from the exhaust gasses entering into it by using a stainless block off insert disc plate in the y-pipe inlet to the egr cooler like the one Elite
diesel sells. This involves less work and less cost to achieve the same results while still retaining the egr cooler, the cooler then just acts like an additional small radiator for coolant but has no exhaust gasses flowing through it.
The well known secret to obtaining the best performance from a diesel engine is airflow. When you have the proper cooled airflow matched with the proper timing and fuel delivery exiting into a free flowing exhaust, you get a very good running truck. Will it run cooler under heavy loads than a truck running with egr? In most cases yes, this is due to the cooling system no longer having to work at getting rid of the egr cooler temps which can be in the 1100-1200F range. It also helps the coolant itself maintain a better condition as its not subjected to those temps. In a way you have slightly enlarged your cooling system with an egr delete.
With proper tuning, a non egr truck can burn clean without any smoke, pull heavy loads and maintain proper fluid and exhaust temps. Just the formation of NOX may be an issue to our emission laws.