Allison Transmission

Hard to know what the problem is, but I would start by checking for diagnostic trouble codes, checking for any related service bulletins from GM, and check to see that the software in the transmission control module is up to date. This will need to go to a dealer for this, or to an independent shop that can perform all of these tasks.

I had the exact same problem with my 02 chevy. The problem was not with the transmission it was the fuel filter. I changed the fuel filter and it runs fine now.

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This may be due to a condition called "turbo lag"