2008 gmc serria 2500 hd is having transmission problems when its pulling a trailer .feels like it goes into neutral engine rpms go up then it makes a boom sound and goes into 2nd or 3rd gear with reduced engine power. The manual part of the gear shifter diplay will not display what gear it is in. Third time. Gmc dealer shop is looking at it but say they haven't seen this code before. P2714 just looking for some feed back. Many thanks for any help. [email protected]
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