ISX15 overheating after vgr turbo installed

[Yady]

Hi my truck was demandated when I purchased it. It also had a K29 turbo in it. Engine brakes weren't working so I decided to install a vgr turbo. It fixed the engine brakes problem. Since I installed the vgr turbo though its been heating up and it takes longer to lower the temp even when I turn the fan on which before would lower the temp right away. Its giving me a check engine light. When I check insite the code is for Exhaust Gas Pressure I. Any thoughts on what could be going on? Thanks in advance.