CHANGE YOUR FUEL FILTER!!! What you're seeing is a limp mode from when the fuel rail pressure relief valve pops. The early LLY motors were famous for it when running a chip. There is a shim kit available to fix it cheaply, but the main cause is a bad fuel filter. What happens is when you dig into it, fuel pressure keeps ramping up and eventually it gets too high and pops the relief valve.

You should be changing the filter at least two times a year. Every oil change would be best. Electronic unit injectors do NOT like dirty fuel. A bad fuel filter will make a Duramax/Allison do weird things. If the pricing of filters is a concern, you can order them online by the case for 1/2 to 2/3 of the price you can get them most local places.